UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

Filed by the Registrant  ☒                              Filed by a Party other than the Registrant  ☐

Check the appropriate box:

Seattle Genetics, Inc.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if Other Than the Registrant)

Payment of Filing Fee (Check the appropriate box)

April 4, 2018

Dear Seattle Genetics Stockholders:

On behalf of Seattle Genetics, Inc., I cordially invite you to attend our 2018 Annual Meeting of Stockholders to be held on Friday, May 18, 2018, at 11:00 a.m., local time, at our principal offices located in Building 3 at 21823 – 30^th Drive SE, Bothell, Washington 98021.

Details of the business to be conducted at the Annual Meeting are given in the Notice of Annual Meeting of Stockholders and the proxy statement.

We are using the Internet as our primary means of furnishing proxy materials to stockholders. Most stockholders will not receive paper copies of our proxy materials. We will instead send these stockholders a notice with instructions for accessing the proxy materials and voting via the Internet. The notice also provides information on how stockholders may obtain paper copies of our proxy materials if they so choose.

Your vote is important. Whether or not you plan to attend the Annual Meeting, it is important that your shares are represented. Please read the proxy statement and vote via the Internet, over the telephone or, if you received a paper proxy card or voting instruction form by mail, by marking, dating, signing and returning the proxy card or voting instruction form, as promptly as possible. Of course, if you attend the Annual Meeting, you will have the right to vote your shares in person.

On behalf of the Board of Directors, I would like to express our appreciation for your continued interest in Seattle Genetics. We look forward to seeing you at the Annual Meeting.

Sincerely,

Clay B. Siegall, Ph.D.

President and Chief Executive Officer

21823 – 30^TH DRIVE SE

BOTHELL, WA 98021

NOTICE OF ANNUAL MEETING OF STOCKHOLDERS

To Be Held May 18, 2018

The 2018 Annual Meeting of Stockholders (the “Annual Meeting”) of Seattle Genetics, Inc., a Delaware corporation (“Seattle Genetics” or the “Company”), will be held on Friday, May 18, 2018 at 11:00 a.m. local time at the principal offices of Seattle Genetics located in Building 3 at 21823 – 30^th Drive SE, Bothell, Washington 98021, for the following purposes:

You can find more information about each of these items, including the nominees for directors, in the accompanying proxy statement.

The Board of Directors has fixed the close of business on March 22, 2018 as the record date for determining the stockholders entitled to notice of and to vote at the Annual Meeting and at any adjournment or postponement thereof.

We cordially invite all stockholders to attend the Annual Meeting in person. However, whether or not you expect to attend the Annual Meeting in person, please ensure your representation and the presence of a quorum at the Annual Meeting by voting via the Internet, over the telephone or, if you received a paper proxy card or voting instruction form by mail, by marking, dating, signing and returning the proxy card or voting instruction form as promptly as possible in the return envelope provided. If you vote via the Internet, over the telephone or by sending in your proxy card or voting instruction form, but then decide to attend the Annual Meeting to vote your shares in person, you may still do so. Your proxy is revocable in accordance with the procedures described in the accompanying proxy statement. Please note that if your shares are held in an account by your broker, bank, or other nominee and you wish to vote at the Annual Meeting, you must notify your broker, bank or other nominee and obtain the proper documentation.

By Order of the Board of Directors,

Jean I. Liu

Corporate Secretary

Bothell, Washington

April 4, 2018

Important Notice Regarding the Availability of Proxy Materials for the Annual Meeting of Stockholders to be Held on May 18, 2018 in Building 3 at 21823 – 30^th Drive SE, Bothell, Washington 98021.

The proxy statement and annual report to stockholders are available at

http://www.edocumentview.com/SGEN

SEATTLE GENETICS, INC.

PROXY STATEMENT FOR THE

2018 ANNUAL MEETING OF STOCKHOLDERS

To Be Held May 18, 2018

Our Board of Directors is soliciting proxies for the 2018 Annual Meeting of Stockholders. This proxy statement contains important information for you to consider when deciding how to vote on the matters brought before the meeting. Please read it carefully.

The Board has set the close of business on March 22, 2018 as the record date for the Annual Meeting. Stockholders of record who owned our common stock on that date are entitled to vote at and attend the Annual Meeting. Each share of common stock is entitled to one vote. There were 158,159,874 shares of common stock outstanding on the record date. Our proxy materials, which include this proxy statement and our 2017 annual report, are first being mailed or made available to stockholders on or about April 4, 2018. This proxy statement and our 2017 annual report are available on the Internet at http://www.edocumentview.com/SGEN.

In this proxy statement:

We summarize below important information with respect to the Annual Meeting.

TIME AND PLACE OF THE ANNUAL MEETING

The Annual Meeting is being held on Friday, May 18, 2018, at 11:00 a.m. local time at our principal offices located in Building 3 at 21823 – 30th Drive SE, Bothell, Washington 98021. Directions to our principal offices may be found at www.seattlegenetics.com.

All stockholders who owned shares of our stock as of March 22, 2018, the record date, may attend and vote on the proposals considered at the Annual Meeting.

PURPOSE OF THE PROXY MATERIALS

Our Board of Directors is soliciting your proxy to vote at the Annual Meeting, including at any adjournments or postponements of the Annual Meeting. This proxy statement describes the proposals on which we would like you, as a stockholder, to vote. It also gives you information on these proposals so that you can make an informed decision, information you may find useful in determining how to vote and information regarding voting procedures.

INTERNET AVAILABILITY OF PROXY MATERIALS

In accordance with the rules of the SEC, we are using the Internet as our primary means of furnishing proxy materials to stockholders. Consequently, most stockholders will not receive paper copies of our proxy materials. We will instead send these stockholders a Notice of Internet Availability of Proxy Materials (the “Notice”) with instructions for accessing the proxy materials, including our proxy statement and 2017 annual report, and voting via the Internet. The Notice also provides information on how stockholders may obtain paper copies of our proxy materials if they so choose. This makes the proxy distribution process more efficient and less costly, and helps conserve natural resources.

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PROPOSALS TO BE VOTED ON AT THIS YEAR’S ANNUAL MEETING AND BOARD RECOMMENDATIONS

At the Annual Meeting, there are four matters scheduled for a vote:

The Board of Directors recommends a vote “FOR” all of the nominees named herein for director and a vote “FOR” each of the other proposals.

VOTING VIA THE INTERNET, BY TELEPHONE OR BY MAIL

Stockholders whose shares are registered with our transfer agent, Computershare Inc., in their own name are record holders also known as stockholders of record. As an alternative to voting in person at the Annual Meeting, a record holder may vote via the Internet, over telephone or, for those stockholders who receive a paper proxy card in the mail, by mailing a completed proxy card.

For those record holders who receive a paper proxy card, instructions for voting via the Internet, over the telephone or by mail are set forth on the proxy card. If you are a stockholder who elects to vote by mail, you should sign and mail the proxy card in the addressed, postage paid envelope that was enclosed with the proxy materials, and your shares will be voted at the Annual Meeting in the manner you direct.

Stockholders whose shares are not registered in their own name with Computershare Inc. are beneficial holders of shares held in street name. Such shares may be held in an account at a bank or at a brokerage firm (your record holder). As the beneficial holder, you have the right to direct your record holder on how to vote your shares, and you will receive instructions from your record holder that must be followed in order for your record holder to vote your shares per your instructions. Many banks and brokerage firms have a process for their beneficial holders to provide instructions via the Internet or by telephone. If Internet or telephone voting is unavailable from your record holder, please complete and return the voting instruction form in the addressed, postage paid envelope provided. If your shares are held beneficially in street name and you have not given your record holder voting instructions, your record holder will not be able to vote your shares with respect to any matter other than ratification of the appointment of Seattle Genetics’ independent registered public accounting firm as explained in more detail below.

For those stockholders who receive a Notice, the Notice provides information on how to access your proxy materials on the Internet, which contains instructions on how to vote via the Internet or by telephone. If you received a Notice, you can request a printed copy of your proxy materials by following the instructions contained in the Notice.

VOTING IN PERSON AT THE ANNUAL MEETING

If you are a stockholder of record, you may vote in person at the Annual Meeting. Whether or not you plan to attend the Annual Meeting, we urge you to vote by proxy to ensure your vote is counted. You may still attend

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the Annual Meeting and vote in person even if you have already voted by proxy. If your shares are held in street name, your shares may be voted by you in person at the Annual Meeting only if you obtain a legal proxy from your record holder giving you the right to vote such shares in person at the Annual Meeting.

REVOCATION OF PROXIES

You may revoke or change a previously delivered proxy at any time before the final vote at the Annual Meeting. If you are the record holder of your shares, you may revoke your proxy in any one of the following ways:

Your most recent proxy card or telephone or Internet proxy is the one that is counted.

If your shares are held by your broker, bank or other agent as a nominee or agent, you should follow the instructions provided by your broker, bank or other agent.

MULTIPLE SETS OF PROXY MATERIALS

If you receive more than one set of proxy materials, or more than one Notice or a combination thereof, your shares may be registered in more than one name or are registered in different accounts. Please follow the voting instructions on each set of proxy materials or Notices to ensure that all of your shares are voted.

QUORUM REQUIREMENT

Shares are counted as present at the Annual Meeting if a stockholder of record either:

The holders of a majority of our issued and outstanding shares of common stock entitled to vote as of the record date must be present at the Annual Meeting (either in person or by proxy) in order to hold the Annual Meeting and conduct business. This is called a “quorum.”

VOTING INSTRUCTIONS; ABSTENTIONS AND BROKER NON-VOTES

If you are the record holder of your shares, you must vote by proxy or attend the Annual Meeting in person in order to vote on the proposals. If the shares you own are held in “street name” by a brokerage firm, your brokerage firm, as the record holder of your shares, is required to vote your shares according to your instructions. In order to vote your shares, you will need to follow the directions your brokerage firm provides you. Many brokers also offer the option of voting via the Internet or over the telephone, instructions for which would be provided by your brokerage firm on your voting instruction form. Under the current rules that govern brokers, if you do not give instructions to your brokerage firm, it will still be able to vote your shares, but only with respect to proposals for which it has discretionary voting authority. A “broker non-vote” occurs when a broker or other holder of record holding shares for a beneficial owner submits a proxy for the Annual Meeting but does not vote on a particular proposal because that holder does not have discretionary voting power with respect to that proposal and has not received instructions from the beneficial owner.

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The election of directors (Proposal No. 1), the amendment and restatement of the 2007 Plan (Proposal No. 3) and the advisory vote on the compensation of our named executive officers (Proposal No. 4) are proposals for which brokers do not have discretionary voting authority. If you do not instruct your broker how to vote with respect to these proposals, your broker may not vote with respect to these proposals and those non-votes will be counted as “broker non-votes.” The ratification of the appointment of PricewaterhouseCoopers LLP as our independent registered public accounting firm (Proposal No. 2) is considered to be discretionary and your brokerage firm will be able to vote on Proposal No. 2 even if it does not receive instructions from you, so long as it holds your shares in its name.

Abstentions and broker non-votes will be treated as shares present for the purpose of determining the presence of a quorum for the transaction of business at the Annual Meeting. Abstentions and broker non-votes are not counted for the purpose of determining the number of votes cast and will therefore not have any effect with respect to any of the proposals.

We encourage you to provide instructions to your brokerage firm by voting your proxy. This ensures that your shares will be voted at the Annual Meeting.

REQUIRED VOTES

Assuming that a quorum is present at the Annual Meeting, the following votes will be required:

We believe that the procedures to be used by the Inspector of Election to count the votes are consistent with Delaware law concerning voting of shares and determination of a quorum.

VOTE SOLICITATIONS

The Board of Directors of Seattle Genetics is soliciting your proxy to vote your shares at the Annual Meeting. We will bear the entire cost of this solicitation of proxies, including the preparation, assembly, printing, and mailing of the Notice, this proxy statement, the proxy card and any additional solicitation material that we may provide to our stockholders. In addition to these proxy materials, Alliance Advisors and our directors, officers and other employees may contact you by telephone, via the Internet, in person or otherwise to obtain your proxy. We have retained Alliance Advisors as a proxy solicitor in connection with the Annual Meeting. We have agreed to pay to Alliance Advisors a fee of $14,000 plus reasonable out-of-pocket expenses incurred in the process of soliciting proxies. Our directors, officers and other employees will not receive any additional compensation for assisting in the solicitation. We will also request brokerage firms, nominees, custodians and fiduciaries to forward proxy materials to the beneficial owners. We will reimburse these entities and our transfer agent for their reasonable out-of-pocket expenses in forwarding proxy materials.

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VOTING PROCEDURES

Votes cast by proxy or in person at the Annual Meeting will be tabulated by a representative of Computershare Inc., our transfer agent, who will act as the Inspector of Election. The Inspector of Election will also determine whether a quorum is present at the Annual Meeting.

Shares properly voted by proxy will be voted at the Annual Meeting. If you specify a choice with respect to any matter to be acted on, the shares will be voted in accordance with that specified choice. If you are the record holder of your shares and you do not specify your vote on each proposal individually when voting via the Internet or over telephone, or if you sign and return a proxy card without giving specific voting instructions, then your shares will be voted as follows:

If any other matter is properly presented at the Annual Meeting, it is the intention of the persons named in the accompanying proxy, referred to in this proxy statement as the “proxy holders,” to vote on those matters in accordance with their best judgment.

PUBLICATION OF VOTING RESULTS

We will announce preliminary voting results at the Annual Meeting. We will publish the final results in a current report on Form 8-K, which we expect to file with the SEC within four business days of the Annual Meeting. If final voting results are not available to us in time to file a Form 8-K within four business days after the meeting, we intend to file a Form 8-K to publish preliminary results and, within four business days after the final results are known to us, file an additional Form 8-K to publish the final results. You can obtain a copy of any of these filings on our website at www.seattlegenetics.com, by contacting our Investor Relations Department at (425) 527-4000, by calling the SEC at (800) 732-0330 for information regarding its public reference room or through the EDGAR system at www.sec.gov.

OTHER BUSINESS

We do not know of any business to be considered at the Annual Meeting other than the proposals described in this proxy statement. If any other business is properly presented at the Annual Meeting, the proxy holders have the authority to vote on such matters at their discretion.

PROPOSALS FOR 2019 ANNUAL MEETING

To have your proposal included in our proxy statement for the 2019 Annual Meeting, you must submit your proposal in writing by December 5, 2018 to Jean I. Liu, Corporate Secretary, Seattle Genetics, 21823 – 30^th Drive SE, Bothell, Washington 98021, and you must comply with all applicable requirements of Rule 14a-8 promulgated under the Securities Exchange Act of 1934, as amended (the “Exchange Act”). However, if the 2019 Annual Meeting is not held between April 18, 2019 and June 17, 2019, then the deadline will be a reasonable time prior to the time we begin to print and send our proxy materials.

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Stockholders wishing to submit proposals or director nominations for our 2019 Annual Meeting that are not to be included in our proxy statement must give timely written notice to our Corporate Secretary in accordance with our bylaws. To be “timely,” written notice must be received by our Corporate Secretary at the above address no earlier than January 18, 2019 and no later than February 17, 2019; provided, however, that in the event the date of the 2019 Annual Meeting is not scheduled to be held between April 18, 2019 and June 17, 2019, then such notice must be received by the later of the 90^th day prior to the date of the 2019 Annual Meeting or the 10^th day following the date on which public announcement or disclosure of the date of the 2019 Annual Meeting is first made. However, in the event that the number of directors to be elected to the Board of Directors is increased and either all of the nominees for director or the size of the increased Board of Directors is not publicly announced or disclosed by Seattle Genetics on or prior to February 7, 2019, a stockholder’s notice to our Corporate Secretary will also be considered timely, but only with respect to nominees for any new positions created by such increase, if the stockholder’s notice is delivered to our Corporate Secretary at the above address not later than the close of business on the 10^th day following the first date all of such nominees or the size of the increased Board of Directors has been publicly announced or disclosed by Seattle Genetics. We also advise you to review our bylaws, which contain additional requirements about advance notice of stockholder proposals and director nominations, including attendance requirements. A stockholder’s notice to our Corporate Secretary must set forth the information required by our bylaws with respect to each nominee or matter the stockholder proposes to bring before the 2019 Annual Meeting, and must be updated not later than ten days after the record date for the determination of stockholders entitled to vote at 2019 Annual Meeting to provide any material changes in the foregoing information. The person presiding at the 2019 Annual Meeting may determine, if the facts warrant, that a nominee or matter has not been properly brought before the meeting and, therefore, may not be considered at the meeting. In addition, the proxy solicited by the Board of Directors for the 2019 Annual Meeting will confer discretionary voting authority with respect to (i) any proposal presented by a stockholder at that meeting for which Seattle Genetics has not been provided with timely notice and (ii) any proposal made in accordance with our bylaws, if the 2019 proxy statement briefly describes the matter and how management proxy holders intend to vote on it, if the stockholder does not comply with the requirements of Rule 14a-4(c)(2) promulgated under the Exchange Act.

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PROPOSAL NO. 1

ELECTION OF DIRECTORS

Our Fourth Amended and Restated Certificate of Incorporation provides that the Board of Directors is divided into three approximately equal classes with staggered three-year terms. As a result, approximately one-third of the total number of directors will be elected every year.

Vacancies on the Board may be filled only by persons elected by a majority of the remaining directors or by the affirmative vote of the holders of a majority of the voting power of the then outstanding shares of our voting stock, provided that newly created directorships resulting from any increase in the number of directors will, unless the Board determines by resolution that any such directorships shall be filled by stockholders, be filled only by a majority of the remaining directors. A director elected by the Board to fill a vacancy (including a vacancy created by an increase in the number of directors) will serve for the remainder of the full term of the class of directors in which the vacancy occurred.

The total number of directors constituting the whole Board of Directors is presently set at nine members. The Class II directors, whose terms expire at the Annual Meeting, are Clay B. Siegall, Felix Baker and Nancy Simonian. The Class III directors, whose terms expire at the 2019 Annual Meeting, are Srinivas Akkaraju, Marc E. Lippman and Daniel G. Welch. The Class I directors, whose terms of office expire at the 2020 Annual Meeting, are Dave W. Gryska, John A. Orwin and Alpna Seth. Dr. Seth was elected as a Class I director by the Board effective March 15, 2018, filling the previously-existing vacancy in Class I and giving effect to the equal apportionment of the members of the Board among the three classes in accordance with our Fourth Amended and Restated Certificate of Incorporation. Our stockholders only elect one class of directors at each annual meeting. The other classes continue to serve for the remainder of their three-year terms.

Clay B. Siegall, Felix Baker and Nancy A. Simonian have been recommended by the Nominating and Corporate Governance Committee of the Board of Directors for election at the Annual Meeting and have been nominated by the Board for election at the Annual Meeting as Class II directors for three-year terms expiring at the 2021 Annual Meeting. Clay B. Siegall, Felix Baker and Nancy A. Simonian were previously elected by the stockholders as Class II directors. Clay B. Siegall, Felix Baker and Nancy A. Simonian are elected by receiving the greatest number of votes cast for their election by holders of common stock that are present in person or represented by proxy at the meeting. Although the election of directors at the Annual Meeting is uncontested and directors are elected by a plurality of votes cast, and we therefore expect that each of the named nominees for director will be elected at the Annual Meeting, under our Corporate Governance Guidelines, any nominee for director is required to submit an offer of resignation for consideration by the Nominating and Corporate Governance Committee if such nominee for director (in an uncontested election) receives a greater number of votes “withheld” from his or her election than votes “for” such election. In such case, the Nominating and Corporate Governance Committee will then consider all of the relevant facts and circumstances and recommend to the full Board the action to be taken with respect to such offer of resignation. Shares represented by executed proxies will be voted, if authority to do so is not withheld, for the election of the three nominees named herein. In the event that any nominee should be unavailable for election as a result of an unexpected occurrence such shares will be voted for the election of such substitute nominees as the Nominating and Corporate Governance Committee may propose. Proxies may not be voted for a greater number of persons than the number of nominees named. Each person nominated for election has consented to being named as a nominee in this proxy statement and has agreed to serve if elected, and management has no reason to believe that any nominee will be unable to serve.

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NOMINEES FOR THE BOARD OF DIRECTORS AND CONTINUING DIRECTORS

The names of the nominees and of the directors whose terms of office will continue after the Annual Meeting, their ages as of April 4, 2018, and certain other information about them are set forth below. The Nominating and Corporate Governance Committee seeks to assemble a Board that, as a group, provides a significant composite mix of experience, knowledge and abilities that will allow the Board to fulfill its responsibilities. To that end, the Nominating and Corporate Governance Committee has identified and evaluated nominees in the broader context of the Board’s overall composition, with the goal of recruiting and retaining members who complement and strengthen the skills of the other members of the Board and who also exhibit integrity, collegiality, sound business judgment and other qualities that the Nominating and Corporate Governance Committee views as critical to effective functioning of the Board. The brief biographies below include information, as of the date of this proxy statement, regarding the specific and particular experience, qualifications, attributes or skills of each nominee and continuing director that led the Nominating and Corporate Governance Committee and the Board to believe that such nominee or continuing director should continue to serve on the Board as of the date of this proxy statement.

There are no family relationships among any of the directors or executive officers of Seattle Genetics.

DIRECTOR NOMINEE PROFILES

Felix Baker, Ph.D. Dr. Baker has served as one of our directors since July 2003 and as our lead independent director since February 2005. Dr. Baker is Co-Managing Member of Baker Bros. Advisors LP. Dr. Baker and his brother, Julian Baker, started their fund management careers in 1994 when they co-founded a biotechnology investing partnership with the Tisch Family. In 2000, they founded Baker Bros. Advisors LP. Dr. Baker holds a B.S. and a Ph.D. in Immunology from Stanford University, where he also completed two years of medical school. In addition to Seattle Genetics, Dr. Baker currently serves as a director of Alexion Pharmaceuticals, Inc. and Genomic Health, Inc., both of which are publicly-traded biotechnology companies. In addition, Dr. Baker previously served as a director of Ardea BioScience, Inc., AnorMED Inc., Conjuchem, Inc., Neurogen Corporation, Synageva BioPharma Corp. and Trimeris, Inc., all of which were publicly-traded companies during Dr. Baker’s service as a director. As a board member and investor in many successful biotechnology companies, Dr. Baker is able to draw on his experience and vision in investing in and building companies to add significant value to Board of Directors discussions and company strategy.

Clay B. Siegall, Ph.D. Dr. Siegall co-founded Seattle Genetics in 1997. He has served as our Chief Executive Officer since November 2002, as our President since June 2000, as one of our directors since

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December 1997 and as our Board chairman since March 2004. Dr. Siegall also served as our Chief Scientific Officer from December 1997 until November 2002. Prior to co-founding Seattle Genetics, Dr. Siegall was with the Bristol-Myers Squibb Pharmaceutical Research Institute from 1991 to 1997, most recently as a Principal Scientist. From 1988 to 1991, Dr. Siegall was a Staff Fellow/Biotechnology Fellow at the National Cancer Institute, National Institutes of Health. Dr. Siegall received a Ph.D. in Genetics from George Washington University and a B.S. in Zoology from the University of Maryland. In addition to Seattle Genetics, Dr. Siegall serves as a director of Ultragenyx Pharmaceutical Inc. and Alder BioPharmaceuticals, Inc., both publicly-traded biotechnology companies. He served as a director of Mirna Therapeutics, Inc., also a publicly-traded biotechnology company from 2013 to 2016. Dr. Siegall’s experience in founding and building Seattle Genetics is integral to our success and our mission. His scientific understanding along with his corporate vision and operational knowledge provide strategic guidance to our management team and the Board of Directors.

Nancy A. Simonian, M.D. Dr. Simonian has served as one of our directors since March 2012. Since July 2012, Dr. Simonian has served as the Chief Executive Officer of Syros Pharmaceuticals, Inc., a publicly-traded life science company focused on gene control therapeutics. From 2001 to October 2011, Dr. Simonian was with Millennium Pharmaceuticals, Inc.: The Takeda Oncology Company (“Takeda”) most recently serving as Chief Medical Officer and Senior Vice President of Clinical, Medical and Regulatory Affairs. From 1995 to 2001, Dr. Simonian was at Biogen (now Biogen Idec) and most recently served as Vice President of Clinical Research where she was responsible for clinical development and medical affairs of the neurology and oncology pipeline, including Avonex^® and Tysabri^®. Dr. Simonian currently serves as on the board of the Biotechnology Innovation Organization (BIO) and the Damon Runyan Foundation and previously served as a director of ArQule, Inc., a publicly traded biotechnology company, and the Personalized Medicine Coalition. Prior to joining the pharmaceutical industry, Dr. Simonian was on the faculty of Massachusetts General Hospital and Harvard Medical School as an assistant professor of neurology. She received a B.A. in Biology from Princeton University and an M.D. from the University of Pennsylvania Medical School. As a current and former senior executive of several other biotechnology companies, Dr. Simonian possesses a strong understanding of the biotechnology industry and the challenges that we must meet in order to develop and commercialize our product candidates.

THE BOARD RECOMMENDS A VOTE FOR ALL THREE OF

THE NOMINEES FOR DIRECTOR NAMED ABOVE.

CONTINUING DIRECTOR PROFILES

Srinivas Akkaraju, M.D., Ph.D. Dr. Akkaraju has served as one of our directors since July 2003. Dr. Akkaraju is a founder and Managing General Partner of Samsara BioCapital. Previously, from April 2013 to February 2016, Dr. Akkaraju served as a General Partner of Sofinnova Ventures. From January 2009 to April 2013, Dr. Akkaraju served as Managing Director of New Leaf Venture Partners. From August 2006 to December 2008, Dr. Akkaraju served as a Managing Director at Panorama Capital, LLC, a private equity firm founded by the former venture capital investment team of J.P. Morgan Partners, LLC, a private equity division of JPMorgan Chase & Co. Panorama Capital advised J.P. Morgan Partners as to its investment in Seattle Genetics. Prior to co-founding Panorama Capital, he was with J.P. Morgan Partners, which he joined in April 2001 and of which he became a Partner in January 2005. From October 1998 to April 2001, he was in Business and Corporate Development at Genentech, Inc. (now a member of the Roche Group), a biotechnology company, most recently as Senior Manager. Prior to joining Genentech, Dr. Akkaraju was a graduate student at Stanford University, where he received an M.D. and a Ph.D. in Immunology. He received his undergraduate degrees in Biochemistry and Computer Science from Rice University. In addition to Seattle Genetics, Dr. Akkaraju serves as a director of Intercept Pharmaceuticals, Inc., Syros Pharmaceuticals, Inc., Versartis, Inc. and aTyr Pharma, Inc., publicly traded biotechnology companies. Previously, Dr. Akkaraju served as a director on the boards of Barrier Therapeutics, Inc., Eyetech Pharmaceuticals, Inc., ZS Pharma Inc. and Synageva Biopharma Corp., all publicly traded biotechnology companies, and Amarin Corporation plc, a foreign publicly traded biotechnology company. Dr. Akkaraju has a strong scientific background coupled with extensive experience in private equity and venture

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capital investing from his work at J.P. Morgan, Panorama Capital, New Leaf and Sofinnova. This combination allows for Dr. Akkaraju to thoroughly understand our technology and provide strong business and strategic expertise.

David W. Gryska Mr. Gryska has served as one of our directors since March 2005. Since October 2014, Mr. Gryska has served as Executive Vice President and Chief Financial Officer of Incyte Corporation, a publicly-traded biopharmaceutical company. From May 2012 to December 2012, Mr. Gryska served as Chief Operating Officer and from August 2012 to December 2012, interim Chief Executive Officer of Myrexis Inc., a publicly-traded biotechnology company. From December 2006 to October 2010, he served as Senior Vice President and Chief Financial Officer of Celgene Corporation. From October 2004 to December 2006, he was a principal at Strategic Consulting Group, where he provided strategic consulting to early-stage biotechnology companies. Mr. Gryska served at Scios, Inc., a biopharmaceutical company, as Senior Vice President and Chief Financial Officer from November 2000 to October 2004, and as Vice President of Finance and Chief Financial Officer from December 1998 to November 2000. Scios was acquired by Johnson & Johnson in 2003. From 1993 to December 1998, he served as Vice President, Finance and Chief Financial Officer at Cardiac Pathways Corporation, a medical device company which was later acquired by Boston Scientific Corporation. Prior to Cardiac Pathways, Mr. Gryska served as a partner at Ernst & Young LLP, an accounting firm. During his eleven years at Ernst & Young LLP, he focused on technology industries, with an emphasis on biotechnology and healthcare companies. Mr. Gryska holds a B.A. in accounting and finance from Loyola University and an M.B.A. from Golden Gate University. In addition to Seattle Genetics, Mr. Gryska serves on the board of PDL BioPharma, Inc., a publicly-traded biotechnology company. With his years of experience as Chief Financial Officer, at Incyte Corporation, Celgene, Scios, and Cardiac Pathways, Mr. Gryska brings to the Board of Directors valuable and relevant experience as a senior financial executive at life sciences and biotechnology companies dealing with financings, mergers, acquisitions and global expansion and other strategic transactions. He also has extensive knowledge of accounting principles and financial reporting rules and regulations, tax compliance and oversight of the financial reporting processes of several large, publicly traded corporations, which assists Mr. Gryska in fulfilling his duties as chair of our Audit Committee.

Marc E. Lippman, M.D. Dr. Lippman has served as one of our directors since June 2000. Since May 2007, Dr. Lippman has served as the Kathleen and Stanley Glaser Professor of Medicine and Chairman of the Department of Medicine at the University of Miami Leonard M. Miller School of Medicine. From January 2008 to October 2017, Dr. Lippman served as the Deputy Director of the Sylvester Comprehensive Cancer Center of University of Miami Leonard M. Miller School of Medicine. Previously, from February 2001 to May 2007 he served as the John G. Searle Professor and Chairman of the Department of Internal Medicine at the University of Michigan School of Medicine. Previously, Dr. Lippman was the Director of the Lombardi Cancer Research Center from July 1988 to February 2001, Professor and Chairman of the Department of Oncology from July 1999 to February 2001 and Professor of Medicine at Georgetown University Medical School in Washington, D.C. from July 1988 to February 2001. He also served as Chief of the Division of Hematology-Oncology at Georgetown University Medical School from July 1995 to February 2001. He was Head of the Medical Breast Cancer Section of the Medicine Branch of the National Cancer Institute from July 1976 to July 1988. Dr. Lippman has authored over 500 peer-reviewed publications and one of the standard texts on breast cancer. He received a B.A., magna cum laude, from Cornell and an M.D. from Yale where he was elected to Alpha Omega Alpha. Dr. Lippman’s extensive experience in treating patients and conducting oncology research at the National Cancer Institute and at the medical schools of the University of Miami, the University of Michigan and Georgetown University provides an important patient perspective and focus on innovation in our development of antibody-based therapies.

John A. Orwin Mr. Orwin has served as one of our directors since January 2014. From June 2013 to June 2017, he served as Chief Executive Officer and member of the board of Relypsa, Inc now an affiliate of Galencia A.G, a Swiss-listed public company. Prior to Relypsa, Mr. Orwin served as President and Chief Operating Officer of Affymax, Inc., a biotechnology company, from April 2010 to January 2011, as their Chief Executive Officer from February 2011 through May 2013 and a member of their board of directors from February 2011 to

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November 2014. From 2005 to April 2010, Mr. Orwin served as Vice President and then Senior Vice President of the BioOncology Business Unit at Genentech, Inc. (now a member of the Roche Group), a biotechnology company, where he was responsible for all marketing, sales, business unit operations and pipeline brand management for Genentech’s oncology portfolio in the United States. From 2001 to 2005, Mr. Orwin served in various executive-level positions at Johnson & Johnson, a life sciences company, overseeing oncology therapeutic commercial and portfolio expansion efforts in the U.S. Prior to such roles, Mr. Orwin held senior marketing and sales positions at various life sciences and pharmaceutical companies, including Alza Corporation (acquired by Johnson & Johnson), Sangstat Medical Corporation (acquired by Genzyme), Rhone-Poulenc Rorer Pharmaceuticals, Inc. (merged with Sanofi-Aventis) and Schering-Plough Corporation (merged with Merck). Mr. Orwin serves as a member of the boards of directors of Array BioPharma Inc. and of Retrophin, Inc., both publicly-traded biopharmaceutical companies. Mr. Orwin also s served on the board of directors of NeurogesX, Inc., a biopharmaceutical company, until July 2013. Mr. Orwin received an M.B.A. from New York University and a B.A. from Rutgers University. Mr. Orwin’s many years of experience as a senior executive gives him a strong understanding of the biotechnology industry and the challenges we must meet in order to continue developing and commercializing ADCETRIS and our product candidates.

Alpna Seth, Ph.D. Dr. Seth has served as one of our directors since March 2018. Dr. Seth currently serves as the Chief Operating Officer of Vir Biotechnology, Inc. Prior to joining Vir in July 2017, Dr. Seth was Senior Vice President and Global Head of the Biosimilars Global Business Unit for Biogen, Inc. headquartered in Zug, Switzerland since 2014. For the period from 1998 through July 2017, Dr. Seth held a range of leadership roles at Biogen in business development, drug development and commercial, including founding Managing Director of Biogen Idec India and Program Executive for several of Biogen’s major cross-functional drug development programs and product launches. Dr. Seth also serves as a director of Bio Techne, a publicly-traded biotechnology company. Dr. Seth holds a Ph.D. in Biochemistry and Molecular Biology from University of Massachusetts Medical School and conducted her post-doctoral research at Harvard University in Immunology and Structural Biology, both as a Howard Hughes Medical Institute Fellow. She is also a 2002 graduate of the Advanced Management Program at Harvard Business School. Dr. Seth brings a breadth of experience in drug development, commercial, international operations and general management.

Daniel G. Welch Mr. Welch has served as one of our directors since June 2007. From January 2015 to February 2018, Mr. Welch served as an Executive Partner of Sofinnova Ventures, a venture capital firm. Mr. Welch served as Chief Executive Officer and President of InterMune, Inc., a formerly publicly-traded biotechnology company, from September 2003 until InterMune’s acquisition by Roche Holdings in September 2014, and, from May 2007 to October 2014, he served in the additional role of Chairman of the Board of InterMune. Before joining InterMune, he was Chairman and Chief Executive Officer of Triangle Pharmaceuticals from 2002 to 2003, which was acquired by Gilead in 2003. Prior to that, he was President of Biopharmaceuticals at Elan Corporation from 2000 to 2002. During his tenure at Elan he was responsible for its U.S. commercial operations, international subsidiaries, R&D and diagnostics businesses. From 1987 to 2000, Mr. Welch served in various senior management roles at Sanofi-Synthelabo, now Sanofi-Aventis, including Vice President of Worldwide Marketing and Chief Operating Officer of the U.S. business. Mr. Welch holds a B.S. from the University of Miami and an M.B.A. from the University of North Carolina. In addition to Seattle Genetics, Mr. Welch serves as a director of Intercept Pharmaceuticals, Inc., Ultragenyx Pharmaceuticals, Inc. and AveXis, Inc., publicly-traded biotechnology companies. Mr. Welch’s global commercial background and strong senior executive experience at a wide range of biotechnology companies, including previously serving as Chairman and Chief Executive Officer of two publicly-traded biotechnology companies, gives him insight into the strategy and planning for a biopharmaceutical company that is valuable to our senior management as well as the other members of our Board of Directors.

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EXECUTIVE OFFICERS

The executive officers of Seattle Genetics who are not also directors of Seattle Genetics, their ages as of April 4, 2018, and certain other information about them are set forth below:

EXECUTIVE OFFICER PROFILES

Todd E. Simpson Mr. Simpson has served as our Chief Financial Officer since October 2005. Previously, Mr. Simpson served from October 2001 to October 2005 as Vice President, Finance & Administration and Chief Financial Officer of Targeted Genetics Corporation, a biotechnology company. From January 1996 to October 2001, Mr. Simpson served as Vice President, Finance & Administration and CFO of Aastrom Biosciences, Inc., a biotechnology company. From August 1995 to December 1995, he served as Treasurer of Integra LifeSciences Corporation, a biotechnology company, which acquired Telios Pharmaceuticals, Inc., in August 1995. From 1992 until its acquisition by Integra, he served as Vice President of Finance and CFO of Telios and in various other finance-related positions. Mr. Simpson is a certified public accountant, and from 1983 to 1992 he practiced public accounting with the firm of Ernst & Young LLP. Mr. Simpson currently serves on the board of directors of Aquinox Pharmaceuticals, Inc., a publicly-traded pharmaceutical company. Mr. Simpson received a B.S. in Accounting and Computer Science from Oregon State University.

Jonathan Drachman, M.D. Dr. Drachman has served as our Chief Medical Officer and Executive Vice President, Research and Development since October 2013. Dr. Drachman previously served as our Senior Vice President, Research and Translational Medicine and various other positions of increasing authority. Prior to joining Seattle Genetics in November 2004, Dr. Drachman was Associate Professor in the Hematology Division, Department of Medicine at the University of Washington in Seattle, where he remains a Clinical Associate Professor of Medicine. He also served as Senior Investigator in the Division of Research and Education and Medical Director of the Umbilical Cord Blood Program at the Puget Sound Blood Center. Dr. Drachman also serves as a director of Calithera Biosciences, Inc., a publicly-traded biotechnology company. Dr. Drachman received a B.A. in Biochemistry from Harvard University and an M.D. from Harvard Medical School. He completed his residency in Internal Medicine and fellowship in Medical Oncology at the University of Washington.

Vaughn B. Himes, Ph.D. Dr. Himes has served as our Chief Technical Officer since August 2016. Dr. Himes joined Seattle Genetics as Executive Vice President, Technical Operations in April 2009 and served as our Executive Vice President, Technical Operations and Process Science from July 2012 until August 2016. Previously, Dr. Himes was with ZymoGenetics, Inc. from November 2005 to March 2009, most recently as Senior Vice President, Technical Operations where his responsibilities included commercial and clinical manufacturing, supply chain and logistics, quality control and process development. From March 2003 to October 2005, he was Vice President, Manufacturing at Corixa, Inc. Prior to that, he held Vice President positions in manufacturing and development at Targeted Genetics and Genovo. Dr. Himes received a Bachelor of Arts in Chemistry from Pomona College in California and a Ph.D. in Chemical Engineering from the University of Minnesota.

Darren S. Cline Mr. Cline has served as our Executive Vice President, Commercial since February 2016. Mr. Cline served as our Senior Vice President, Commercial from February 2015 and prior to that as our Vice

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President, Marketing, Managed Markets and Reimbursement. Prior to joining Seattle Genetics in December 2010, Mr. Cline served as Vice President, Market Access at InterMune, Inc. (subsequently acquired by Roche Holdings) from October 2009 to July 2010, where he was responsible for managed markets access and coverage strategy for the anticipated launch of pirfenidone. Prior to InterMune, Mr. Cline served as Executive Director of Sales at Alexion Pharmaceuticals, Inc., a publicly traded biotechnology company, from October 2006 to October 2009, where he played an integral role in the successful launch of Soliris^® in the United States. Prior to Alexion, Mr. Cline served in various sales, marketing and managed markets leadership positions at Amgen Inc., a publicly traded biotechnology company. Mr. Cline received a B.S. degree in Marketing from San Diego State University and an M.B.A. from Pepperdine University.

Jean I. Liu, J.D. Ms. Liu has served as our General Counsel, Executive Vice President, Legal Affairs and Corporate Secretary since November 2014. Prior to that, she served as Vice President and General Counsel of Halozyme Therapeutics, Inc., a publicly traded biotechnology company, from November 2011 to November 2014. From 1998 to 2011, she was with Durect Corporation, a publicly traded biotechnology company, where she served in positions of increasing responsibility, including most recently Chief Legal Officer and Corporate Secretary. Prior to Durect, Ms. Liu was with the law firms of Pillsbury, Madison & Sutro (now Pillsbury Winthrop) and Venture Law Group where she focused on broad areas of legal advisory for early stage companies, including technology transfer, licensing, patents, and copyright and trademark litigation. Ms. Liu received her B.S. in Cellular and Molecular Biology with highest distinction from the University of Michigan, her M.S. in Biology from Stanford University and her J.D. from Columbia University where she was a Harlan Fiske Stone Scholar.

INDEPENDENCE OF THE BOARD OF DIRECTORS

As required under the listing standards of The Nasdaq Stock Market, a majority of the members of a listed company’s board of directors must qualify as “independent” as defined in Rule 5605(a)(2) of the Nasdaq listing standards, as affirmatively determined by the board of directors. Our Board of Directors consults with our internal and outside counsel to ensure that the Board of Directors’ determinations are consistent with all relevant laws and regulations regarding the definition of “independent,” including those set forth in pertinent Nasdaq listing standards.

Management has reviewed the directors’ responses to a questionnaire asking about their transactions, relationships and arrangements with Seattle Genetics (and those of their immediate family members) and other potential conflicts of interest. Other than as described in this paragraph, these questionnaires did not disclose any transactions, relationships or arrangements that could impact the independence of our directors. After reviewing this information, our Board of Directors has determined that all of our directors are independent directors within the meaning of the applicable Nasdaq listing standards except for Clay B. Siegall, our President and Chief Executive Officer. The Board of Directors also considered Dr. Baker’s role as a Co-Managing Member of Baker Brothers Investments, and the relationship Seattle Genetics has with Baker Brothers Investments and affiliated entities as significant stockholders in making the determination that Dr. Baker is independent. The Board of Directors also considered Dr. Simonian’s past employment with Takeda and the relationship Seattle Genetics has with Takeda for development of ADCETRIS^® (brentuximab vedotin) in making the determination that Dr. Simonian is independent.

BOARD LEADERSHIP STRUCTURE AND RISK OVERSIGHT

Board Leadership Structure

Our Board of Directors has chosen to combine the principal executive officer and Board chairman positions and, in addition, has appointed a separate lead independent director. Dr. Siegall has served as our principal executive officer and Board chairman since 2004. At the present time, the independent directors believe that Dr. Siegall’s in-depth knowledge of our operations and vision for our development make him the best-qualified

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director to serve as Board chairman. We believe that combining the positions of chief executive officer and Board chairman provides a single, clear chain of command to execute our strategic initiatives and business plans. In addition, we believe that a combined chief executive officer/Board chairman is better positioned to act as a bridge between management and the Board, facilitating the regular flow of information. We also believe that it is advantageous to have a Board chairman with an extensive history with and knowledge of Seattle Genetics (as is the case with our chief executive officer) as compared to an independent Board chairman with less direct involvement.

The position of lead independent director has been structured to serve as an effective balance to a combined chief executive officer/Board chairman. In addition, we believe that having a lead independent director, who is independent of management, creates an environment that is more conducive to objective evaluation and oversight of management’s performance, increasing management accountability and improving the ability of the Board of Directors to monitor whether management’s actions are in the best interests of Seattle Genetics and its stockholders. Since February 2005, Felix Baker has served as the lead independent director of the Board. His duties include, among others:

Board Risk Oversight

Our Board of Directors has overall responsibility for risk oversight with a focus on the most significant risks facing Seattle Genetics. Throughout the year, the Board and the committees to which it has delegated responsibility dedicate a portion of their meetings to reviewing and discussing specific risk topics in greater detail. Strategic and operational risks are presented and discussed in the context of the Chief Executive Officer’s report on operations to the Board at regularly scheduled Board meetings and at presentations to the Board and its committees by the respective committee chairmen, our Chief Financial Officer, our General Counsel and Executive Vice President, Legal Affairs, and other officers.

The Board has delegated responsibility for the oversight of specific risks to Board committees as follows:

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MEETINGS AND COMMITTEES OF THE BOARD OF DIRECTORS

During 2017, the Board met five times and acted by written consent one time. On at least a quarterly basis, the Board meets in executive sessions of independent directors without management present. The Board has several committees, including a Compensation Committee, an Audit Committee and a Nominating and Corporate Governance Committee. During 2017, each of our directors attended at least 75% of the aggregate of Board and applicable committee meetings on which he or she served during 2017 for the period that he or she was a director or committee member.

Information about the Compensation Committee

The Compensation Committee consists of Felix Baker (chairman), John A. Orwin and Daniel G. Welch. The Board of Directors has determined that all of the members of the Compensation Committee currently serving are “independent” as that term is defined in Rule 5605(a)(2) of the Nasdaq listing standards. In determining whether Dr. Baker, Mr. Orwin and Mr. Welch are independent within the meaning of Nasdaq listing standards pertaining to membership of the Compensation Committee, our Board of Directors determined that, based on its consideration of factors specifically relevant to determining whether any such director has a relationship to Seattle Genetics that is material to that director’s ability to be independent from management in connection with the duties of a compensation committee member, no member of the Compensation Committee has a relationship that would impair that member’s ability to make independent judgments about our executive compensation. In particular, our Board of Directors considered, among other things, the source of each member’s compensation, including compensation paid to such member by us, and also considered Dr. Baker’s role as a Co-Managing Member of Baker Brothers Investments, and the relationship Seattle Genetics has with Baker Brothers Investments and affiliated entities as significant stockholders and determined that such compensation and affiliation, as applicable, would not impair the applicable member’s ability to make independent judgments about our executive compensation. In the case of Dr. Baker, our Board of Directors determined that, given his affiliation with our largest stockholder, his interests are aligned with other stockholders in seeking an appropriate executive compensation program for Seattle Genetics.

The Compensation Committee held two meetings and acted by written consent twice during 2017. The functions of the Compensation Committee are to establish and administer our policies regarding annual executive salaries, cash incentives and long-term equity incentives. The Compensation Committee also administers our 1998 Stock Option Plan, our 2007 Plan, and Amended and Restated 2000 Employee Stock Purchase Plan, as well as our Senior Executive Annual Bonus Plan and special long-term incentive plans. The Compensation Committee also reviews with management our Compensation Discussion and Analysis and considers whether to recommend that it be included in proxy statements and other filings. The Compensation Committee operates under a written charter setting forth the functions and responsibilities of the committee. A copy of the Compensation Committee charter can be viewed on our website at www.seattlegenetics.com. Under its charter, the Compensation Committee has the authority, in its sole discretion, to retain (or obtain the advice of) any compensation consultant, legal counsel or other adviser to assist it in the performance of its duties. In addition, under its charter, the Compensation Committee may form, and delegate authority to, subcommittees as appropriate. The Compensation Committee also has the direct responsibility for the appointment, compensation and oversight of the work of any advisers retained or engaged by the Compensation Committee. Finally, the Compensation Committee has the sole authority to approve the reasonable fees and the other terms and conditions of the engagement of any such advisor, including authority to terminate the engagement. We must provide for appropriate funding, as determined by the Compensation Committee, for the payment of reasonable compensation to any such adviser retained by the Compensation Committee.

For information regarding our processes and procedures for the consideration and determination of executive and director compensation, please see “Compensation of Executive Officers—Compensation Discussion and Analysis” and “—Director Compensation,” respectively.

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Information about the Audit Committee

The Audit Committee consists of David W. Gryska (chairman), John A. Orwin and Daniel G. Welch. The Board of Directors has determined that all of the members of the Audit Committee are “independent” within the meaning of Rules 5605(c)(2)(A)(i) and (ii) of the Nasdaq listing standards. The Board of Directors has determined that Mr. Gryska is an “audit committee financial expert” as defined in Item 407(d)(5)(ii) of Regulation S-K.

The Audit Committee held six meetings during 2017. Among its responsibilities, the Audit Committee appoints and establishes the fees for our independent registered public accounting firm, reviews and approves the procedures we use to prepare our periodic reports, reviews our critical accounting policies, reviews the independence of the independent registered public accounting firm, monitors the effectiveness of the audit effort and oversees our financial and accounting organization and our system of internal accounting controls. The Audit Committee operates under a written charter setting forth the functions and responsibilities of the committee, which is reviewed annually and amended as necessary by the Audit Committee and the Board of Directors to ensure compliance with all applicable laws and regulations, including the Sarbanes-Oxley Act of 2002 and corporate governance standards adopted by Nasdaq. A copy of the Audit Committee charter can be viewed on our website at www.seattlegenetics.com.

Information about the Nominating and Corporate Governance Committee

The Nominating and Corporate Governance Committee consists of Nancy A. Simonian (chair), Felix Baker and Marc E. Lippman. The Board of Directors has determined that all of the members of the Nominating Committee are “independent” as that term is defined in Rule 5605(a)(2) of the Nasdaq listing standards.

The Nominating and Corporate Governance Committee met twice during 2017. The Nominating and Corporate Governance Committee is responsible for identifying individuals qualified to serve as members of the Board of Directors, recommending nominees to the Board for election as directors of Seattle Genetics and as members of the committees of the Board of Directors, as well as developing and making recommendations to the Board’s Corporate Governance Guidelines and providing oversight with respect to corporate governance and ethical conduct. The Nominating and Corporate Governance Committee operates under a written charter setting forth the functions and responsibilities of the committee. A copy of the Nominating and Corporate Governance Committee charter can be viewed on our website at www.seattlegenetics.com.

The Nominating and Corporate Governance Committee assesses many characteristics and diversity considerations when reviewing director candidates and these characteristics are set forth in our Corporate Governance Guidelines. Among the characteristics to be considered are such person’s professional background, business experience, judgment and integrity, familiarity with the biotechnology industry, applicable expertise and the interplay of the candidate’s experience and skills with those of other Board members. In determining whether to recommend a director for re-election, the Nominating and Corporate Governance Committee also considers the director’s past attendance at meetings and participation in and contributions to the activities of the Board and its committees, as well as the nature and time involved in a director’s service on other boards. The Nominating and Corporate Governance Committee seeks nominees with a broad diversity of experience, professions, skills, geographic representation and backgrounds; however, the Nominating and Corporate Governance Committee does not assign specific weights to particular criteria and no particular criterion is necessarily applicable to all prospective nominees. We believe that the backgrounds and qualifications of our directors, considered as a group, should provide a significant composite mix of experience, knowledge and abilities that will allow the Board to fulfill its responsibilities. Nominees are not discriminated against on the basis of age, race, religion, national origin, sexual orientation, disability or any other basis proscribed by law.

The Nominating and Corporate Governance Committee identifies nominees by first evaluating the current members of the Board willing to continue in service. Current members of the Board with skills and experience

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that are relevant to our business and who are willing to continue in service are considered for re-nomination. If there is a vacancy on the Board as a result of a resignation or otherwise, or if the Board decides not to nominate a member for re-election or decides to add a member to the Board, the Nominating and Corporate Governance Committee identifies the desired skills and experience of a new nominee in light of the criteria above and the Board’s needs. Current members of the Board are asked to submit suggestions as to individuals meeting the criteria described above. To date, we have not engaged third parties to identify or evaluate or assist in identifying potential nominees, although we may in the future decide to retain a third-party search firm.

In accordance with our bylaws and applicable law, nominations for directors may be made by any stockholder of record entitled to vote for the election of directors at stockholder meetings held for such purpose. The requirements a stockholder must follow for nominating persons for election as directors are set forth in our bylaws and under the heading “Proposals for 2019 Annual Meeting.” The Nominating and Corporate Governance Committee will also consider director candidates recommended by stockholders. In order to recommend director candidates to the Nominating and Corporate Governance Committee, stockholders should follow the procedures in our bylaws for director nominations. If a stockholder complies with these procedures for recommending persons for election as directors, the Nominating and Corporate Governance Committee will conduct the appropriate and necessary inquiries into the backgrounds, qualifications and skills of the recommended candidates and, in the exercise of the Nominating and Corporate Governance Committee’s independent judgment in accordance with the policies and procedures adopted in the Nominating and Corporate Governance Committee’s charter, will determine whether to recommend the candidate(s) recommended by the stockholders to the Board for inclusion in the list of candidates for election as directors at the next stockholder meeting held to elect directors. The Nominating and Corporate Governance Committee does not intend to alter the manner in which it evaluates director candidates based on whether or not the candidate was recommended by a stockholder.

Annual Meeting Attendance

Although we do not have a formal policy regarding attendance by members of the Board of Directors at our Annual Meetings of Stockholders, directors are encouraged to attend. All of our directors then serving attended the 2017 Annual Meeting of Stockholders.

CERTAIN OTHER CORPORATE GOVERNANCE MATTERS

Communications with the Board of Directors

Our Board of Directors currently does not have a formal process for stockholders to send communications to the Board of Directors. Nevertheless, efforts are made to ensure that the views of stockholders are heard by the Board or individual directors, as applicable, and that appropriate responses are provided to stockholders on a timely basis. The Board does not recommend that formal communication procedures be adopted at this time because it believes that informal communications are sufficient to communicate questions, comments and observations that could be useful to the Board. However, stockholders wishing to formally communicate with the Board of Directors may send communications directly to Seattle Genetics, Inc., Attention: Investor Relations, 21823 – 30^th Drive SE, Bothell, Washington 98021, and the communication will be forwarded, as appropriate. If the communication regards a stockholder proposal to be considered at an annual meeting of stockholders, the methods and timing for submitting a stockholder proposal are covered under the heading “Proposals for 2019 Annual Meeting.”

Corporate Governance Guidelines

As a part of the Board’s commitment to building long-term stockholder value with an emphasis on corporate governance, the Board has adopted a set of Corporate Governance Guidelines, which guides the operation of the Board and its committees. Our Corporate Governance Guidelines cover, among other topics, Board composition, structure and functioning, Board membership criteria, director independence, Board self-evaluations, committees

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of the Board, Board access to management and independent advisers, stock ownership guidelines for members of the Board and our executive officers, and succession and leadership development. A copy of the Corporate Governance Guidelines can be viewed on our website at www.seattlegenetics.com.

Code of Ethics

The Board of Directors has adopted a Code of Conduct and Business Ethics (our “Code of Ethics”), for all directors, officers and employees of Seattle Genetics, Inc. A copy of the Code of Ethics can be viewed on our website at www.seattlegenetics.com. We intend to satisfy the disclosure requirement under Item 5.05 of Form 8-K regarding an amendment to, or waiver from, a provision of the Code of Ethics by posting such information on our website at the website address specified above.

Whistleblower Policy

Seattle Genetics has adopted a Whistleblower Policy applicable to its employees that provides for protection from retaliation or discrimination by Seattle Genetics due to reporting issues relating to concerns involving questionable accounting or auditing matters and compliance with applicable laws and regulations.

DIRECTOR COMPENSATION

Cash Compensation. Our non-employee directors received an annual retainer of $50,000 in 2017 for their service on the Board, plus reimbursement for out-of-pocket expenses incurred in connection with attendance at Board and Board committee meetings, and our lead independent director received an additional retainer of $25,000 in 2017. Our non-employee directors also received the following additional annual retainers for service on committees of the Board in 2017:

If a nonemployee director has not served on the Board or a Board committee for the full year, the Board and any applicable Board committee retainers may be prorated for the portion of the year served.

Equity Compensation. Our Board has established a policy of providing each person who becomes a nonemployee director of Seattle Genetics an initial nonstatutory stock option to purchase shares of our common stock and an initial restricted stock unit (“RSU”) grant. Such grants are made under our 2007 Plan. These initial awards are granted on the date on which a recipient first becomes a nonemployee director of Seattle Genetics. In 2017, nonemployee directors were eligible for an initial nonstatutory stock option to purchase 14,250 shares of common stock and an initial RSU grant covering 5,750 shares of common stock. This initial option grant vests as to 25% of the underlying shares on the first anniversary of the grant date and ratably thereafter on a monthly basis until such grant is fully vested on the fourth anniversary of the grant date, and the initial RSU award vests in full on the third anniversary of the grant date, subject in both cases to continued service. In connection with her appointment to our Board effective March 15, 2018, Dr. Seth was granted a nonstatutory stock option to purchase 14,250 shares of common stock and an RSU grant covering 5,750 shares of common stock.

In addition, effective on the date of each annual meeting of stockholders, each nonemployee director is granted an annual nonstatutory stock option to purchase shares of common stock and an annual RSU grant under the 2007 Plan if, on such date, he or she had served on the Board for at least six months. In 2017, each of our non-employee directors received an annual option to purchase 9,260 shares of common stock and an annual RSU grant covering 3,700 shares of common stock, effective on the date of our Annual Meeting. With the exception of Dr. Seth, each of our nonemployee directors is expected to receive an annual option to purchase 9,260 shares of common stock and an annual RSU grant covering 3,700 shares of common stock under the 2007 Plan effective on the date of the 2018 Annual Meeting.

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The annual option award and annual RSU awards made to each of our directors in 2017 will vest on May 18, 2018. In addition, all non-employee directors would receive full acceleration of vesting of any outstanding options or RSU awards under the 2007 Plan and the Directors’ Plan, as applicable, immediately prior to a change in control of Seattle Genetics. The exercise price of options granted to our directors is equal to the fair market value of our common stock on the Nasdaq Global Select Market on the effective date of grant. Options granted to non-employee directors under the 2007 Plan and the Directors’ Plan have ten year terms and remain exercisable for up to three months following the grantee’s termination of service, unless such termination is a result of death or disability, in which case the options remain exercisable for up to a twelve-month period (or such lesser period as is determined by the Board). Although we anticipate that our Board of Directors will continue our equity compensation arrangements for non-employee directors on the same terms as described above, it is within the Board’s discretion to review our equity compensation arrangements for non-employee directors, and the Board may determine to implement new or revised equity compensation arrangements for our non-employee directors that differ from those described above.

In order to align the interests of the directors with Seattle Genetics’ stockholders, our Corporate Governance Guidelines state that all non-employee directors should, not later than December 31^st of the year during which the applicable director achieves his or her fifth anniversary as a non-employee director, own, directly or indirectly, a number of shares of Seattle Genetics common stock with a value not less than three times the annual cash retainer paid by Seattle Genetics to such director for service on the Board, and thereafter such director should continue to own a number of shares with such value until he or she is no longer a director. The Nominating and Corporate Governance Committee used December 31, 2017 as the date to assess compliance with these director ownership guidelines. All of our non-employee directors serving as of such date were in compliance with these guidelines.

Processes and Procedures for Determining Director Compensation. Effective as of February 9, 2018, the responsibility for reviewing director compensation and recommending changes to the Board is vested in the Compensation Committee per its charter. During 2017 this authority was vested in the Nominating and Corporate Governance Committee. It has been the practice of the Nominating and Corporate Governance Committee to seek input from outside compensation consultants as it deems appropriate. For example, in October 2016, Compensia, Inc., our Compensation Committee’s compensation consultant, conducted a survey of director compensation to compare our director compensation to director compensation to our peer group companies. As a result of that survey, we adjusted the initial equity compensation of our nonemployee directors to approximate the 50^th percentile of compensation received by members of the boards of directors of our peer companies. We review our peer group companies periodically and our peer group utilized for purposes of the October 2016 Compensia survey was as follows:

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Director Compensation Table. The following table sets forth all of the compensation awarded to or earned by each person who served as a nonemployee director during 2017. Dr. Siegall, our only employee director, receives no compensation for Board service but is reimbursed for reasonable and customary travel expenses. Dr. Siegall’s compensation is described under “Compensation of Executive Officers” below.

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SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

The following table sets forth information as of March 12, 2018 (except as noted) regarding the beneficial ownership of our common stock by each director (including each nominee for director), by each person or group of affiliated persons known to us to beneficially own five percent or more of our outstanding common stock, by each named executive officer and by all executive officers and directors as a group. Unless otherwise indicated, the address of the individuals and entities below is c/o Seattle Genetics, Inc., 21823 – 30^th Drive SE, Bothell, WA 98021.

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SECTION 16(a) BENEFICIAL OWNERSHIP REPORTING COMPLIANCE

Section 16(a) of the Exchange Act requires our directors, our executive officers and persons who own more than ten percent of our common stock to file initial reports of ownership and changes in ownership of our common stock. These reporting persons are required by SEC regulations to furnish us with copies of all Section 16 reports they file. To our knowledge, based primarily on our review of the copies of such reports received or written representations from certain of these reporting persons that no other reports were required, we believe that during the fiscal year ended December 31, 2017, all of these reporting persons complied with all applicable filing requirements.

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PROPOSAL NO. 2

RATIFICATION OF APPOINTMENT OF INDEPENDENT REGISTERED

PUBLIC ACCOUNTING FIRM

Our Audit Committee has selected PricewaterhouseCoopers LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2018. PricewaterhouseCoopers LLP has served as our independent registered public accounting firm since June 1998. A representative of PricewaterhouseCoopers LLP is expected to be present at the Annual Meeting. This representative will have an opportunity to make a statement and will be available to respond to appropriate questions.

Stockholder ratification of the appointment of PricewaterhouseCoopers LLP as our independent registered public accounting firm is not required by our bylaws or other governing documents. However, the Board is submitting the appointment of PricewaterhouseCoopers LLP to the stockholders for ratification as a matter of good corporate governance. While the Audit Committee is not bound by a vote either for or against the proposal, it will consider a vote against PricewaterhouseCoopers LLP by the stockholders in selecting our independent registered public accounting firm in the future. Even if the stockholders do ratify the appointment, the Audit Committee in its discretion may direct the appointment of a different independent registered public accounting firm at any time during the year if it believes that such a change would be in the best interests of Seattle Genetics and its stockholders.

Stockholder approval of this Proposal No. 2 will require the affirmative vote of a majority of the votes cast in person or by proxy at the Annual Meeting.

ON BEHALF OF THE AUDIT COMMITTEE, THE BOARD RECOMMENDS A VOTE FOR

THIS PROPOSAL NO. 2

Independent Registered Public Accounting Firm Fees

PricewaterhouseCoopers LLP served as our independent registered public accounting firm for 2016 and 2017 and their aggregate fees for services rendered were as follows:

Audit Fees. Audit fees represent fees for professional services provided in connection with the audit of our financial statements and review of our quarterly financial statements and audit services provided in connection with other statutory or regulatory filings. In 2017, these fees also included service to support our Oracle Enterprise Resource Planning (“ERP”) software implementation, acquisition of a pharmaceutical manufacturing facility in Bothell, Washington and Immunomedics transaction.

Audit-Related Fees. Audit-related fees consist of fees billed for assurance and related services that are reasonably related to the performance of the audit or review of our financial statements and are not reported under “Audit Fees.” In 2017, these fees related to support of our Oracle ERP implementation. There were no audit-related fees billed to Seattle Genetics for services rendered during 2016.

Tax Fees. Tax fees principally included tax compliance, tax advice and tax planning fees. There were no tax fees billed to Seattle Genetics for services rendered during 2016 or 2017.

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All Other Fees. All other fees include any fees billed that are not audit, audit related, or tax fees. In 2016 and 2017, these fees related to accounting research software.

Pre-Approval Policies and Procedures

In October 2006, the Audit Committee adopted an Audit and Audit-Related Services Pre-Approval Policy (the “Policy”), which sets forth the procedures and the conditions pursuant to which services proposed to be performed by the independent registered public accounting firm may be pre-approved. Proposed services either may be pre-approved by the Audit Committee without consideration of specific case-by-case services (i.e., general pre-approval) or require the specific pre-approval of the Audit Committee (i.e., specific pre-approval). The Audit Committee believes that the combination of these two approaches has resulted in an effective and efficient procedure to pre-approve services performed by the independent registered public accounting firm. As set forth in the Policy, unless a type of service has received general pre-approval, it will require specific pre-approval by the Audit Committee if it is to be provided by the independent registered public accounting firm. Any proposed services exceeding pre-approved cost levels or budgeted amounts will also require specific pre-approval by the Audit Committee. In addition, the Audit Committee has delegated to the Chair of the Audit Committee the authority to pre-approve services not prohibited by the Policy to be performed by our independent registered public accounting firm and associated fees up to $25,000, provided that the Chair is required to report any decision to pre-approve such audit-related or non-audit services and fees to the full Audit Committee for ratification at its next regular meeting. All audit-related and non-audit related services performed by our independent registered public accounting firm in 2017 were pre-approved.

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AUDIT COMMITTEE REPORT (1)

The Audit Committee of the Board of Directors is currently comprised of three independent directors and operates under a written charter originally adopted by the Board of Directors in March 2001, which charter is reviewed on an annual basis and amended as necessary by the Board of Directors upon recommendation by the Audit Committee.

The members of the Audit Committee are currently David W. Gryska (chairman), John A. Orwin and Daniel G. Welch. Each of the members of the Audit Committee is an “independent director” as currently defined in Rules 5605(c)(2)(A)(i) and (ii) of the Nasdaq listing standards and Rule 10A-3 of the Exchange Act. The Board of Directors has also determined that David W. Gryska is an “audit committee financial expert” as described in applicable rules and regulations of the SEC.

The Audit Committee appoints an accounting firm as our independent registered public accounting firm. The independent registered public accounting firm is responsible for performing an independent audit of our financial statements in accordance with the standards of the Public Company Accounting Oversight Board, or PCAOB, and issuing a report thereon. Management is responsible for our internal controls and the financial reporting process. The Audit Committee is responsible for monitoring and overseeing these processes.

The Audit Committee held five meetings and acted by written consent once during 2017. The meetings were designed to provide information to the Audit Committee necessary for it to conduct its oversight function of the external financial reporting activities and audit process of Seattle Genetics, and to facilitate and encourage communication between the Audit Committee, management and our independent registered public accounting firm, PricewaterhouseCoopers LLP. Management represented to the Audit Committee that our financial statements were prepared in accordance with accounting principles generally accepted in the United States of America. The Audit Committee reviewed and discussed the audited financial statements for 2017 with management and the independent registered public accounting firm. The Audit Committee also instructed the independent registered public accounting firm that the Audit Committee expects to be advised if there are any subjects that require special attention.

The Audit Committee discussed with the independent registered public accounting firm the matters required to be discussed by Auditing Standard No. 16, Communications with Audit Committees, as adopted by the PCAOB.

The Audit Committee has also received the written disclosures and the letter from the independent registered public accounting firm, PricewaterhouseCoopers LLP, required by applicable requirements of the PCAOB regarding the independent registered public accounting firm’s communications with the Audit Committee concerning independence, and has discussed with PricewaterhouseCoopers LLP that firm’s independence.

Based on its review of the audited financial statements and the various discussions noted above, the Audit Committee recommended to the Board of Directors that the audited financial statements and the audited assessment of internal control over financial reporting be included in our Annual Report on Form 10-K for the fiscal year ended December 31, 2017.

The Audit Committee of the Board of Directors of Seattle Genetics, Inc.:

David W. Gryska (chairman)

John A. Orwin

Daniel G. Welch

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PROPOSAL NO. 3

APPROVAL OF THE AMENDMENT AND RESTATEMENT OF

THE SEATTLE GENETICS, INC.

AMENDED AND RESTATED 2007 EQUITY INCENTIVE PLAN

The Board approved an amendment and restatement of the Seattle Genetics, Inc. Amended and Restated 2007 Equity Incentive Plan (the “2007 Plan”) in March 2018, subject to stockholder approval. Throughout this proxy statement, we refer to the 2007 Plan, as amended and restated by the Board in March 2018, as the “Restated 2007 Plan”.

In this Proposal No. 3, we are requesting stockholder approval of the Restated 2007 Plan in order to:

Why We Recommend That You Vote for the Restated 2007 Plan

Equity Awards Are an Important Part of Our Compensation Philosophy

The Restated 2007 Plan is critical to our ongoing effort to build stockholder value. As discussed in this proxy statement under the heading “Compensation of Executive Officers—Compensation Discussion and Analysis”, equity awards are central to our compensation program. Equity compensation represents a significant percentage of the at-risk, or variable, portion of our executive officers’ compensation arrangements. We believe that it is appropriate to align the interests of our executive officers with those of our stockholders to achieve and sustain long-term stock price growth. Additionally, equity awards represent a significant portion of the compensation we pay to non-employee members of the Board, as well as employees below the executive officer level.

The Board believes we must continue to offer a competitive equity compensation program in order to attract, retain and motivate the extraordinarily talented employees necessary for our continued growth and success. The share reserve of the Restated 2007 Plan is structured to ensure that we have a sufficient number of shares to continue to utilize a broad array of equity incentives in order to secure and retain the services of our and our affiliates’ employees and directors, and to provide incentives for such persons to exert maximum efforts toward our success.

In the event that our stockholders do not approve this Proposal No. 3, the Restated 2007 Plan will not become effective and the 2007 Plan will continue in its current form. However, without the Restated 2007 Plan, we believe that the shares available for grant under the 2007 Plan will be insufficient to meet our anticipated employee recruiting and retention needs.

We Manage Our Equity Award Use Carefully and Dilution Is Reasonable

We manage our long-term stockholder dilution by limiting the number of equity awards granted annually. The Board carefully monitors our annual burn rate, dilution, and equity expense to ensure that we maximize stockholders’ value by granting only the appropriate number of equity awards necessary to attract, reward, and retain employees.

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The following table shows our responsible burn rate history.

In evaluating whether to approve the Restated 2007 Plan, the Compensation Committee reviewed certain forecasts of stock awards for issuance under the Restated 2007 Plan. Management presented the forecasts below for the periods indicated.

As of March 22, 2018 there were 158,159,874 shares of our common stock outstanding. The closing price of our common stock as reported on the Nasdaq Global Select Market as of March 22, 2018 was $53.21 per share.

The Size of Our Share Reserve Request Is Reasonable

If our request to increase the share reserve of the 2007 Plan by 6,000,000 shares is approved, we will have approximately 8,900,000 shares available for grant under the Restated 2007 Plan after our 2018 Annual Meeting, which we anticipate being a two-year pool of shares and necessary to provide a predictable amount of equity for attracting, retaining, and motivating employees and other service providers.

The Restated 2007 Plan Combines Compensation and Governance Best Practices

The Restated 2007 Plan includes provisions that are designed to protect our stockholders’ interests and to reflect corporate governance best practices including:

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Summary of Material Changes and Terms in the Restated 2007 Plan

The Restated 2007 Plan contains the following material changes from the 2007 Plan:

The other material terms of the Restated 2007 Plan will remain the same as in the 2007 Plan as follows:

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Note Regarding Forecasts and Forward-Looking Statements

We do not as a matter of course make public forecasts as to our total shares outstanding and utilization of various equity awards due to the unpredictability of the underlying assumptions and estimates. In particular, the forecasts set forth above in this Proposal No. 3 include embedded assumptions regarding stock option exercises which are highly dependent on the public trading price of our common stock and other factors, which we do not control and, as a result, we do not as a matter of practice provide forecasts. In evaluating these forecasts, the Board recognized the high variability inherent in these assumptions.

However, we have included above a summary of these forecasts to give our stockholders access to certain information that was considered by the Board for purposes of evaluating the approval of the Restated 2007 Plan. These forecasts reflect various assumptions regarding our future operations.

The inclusion of the forecasts set forth above should not be regarded as an indication that these forecasts will be predictive of actual future outcomes, and the forecasts should not be relied upon as such. Neither we nor any other person makes any representation to any of our stockholders regarding actual outcomes compared to the information contained in the forecasts set forth above. Although presented with numerical specificity, the forecasts are not fact and reflect numerous assumptions and estimates as to future events made by our management that our management believed were reasonable at the time the forecasts were prepared and other factors such as industry performance and general business, economic, regulatory, market and financial conditions, as well as factors specific to our business, all of which are difficult to predict and many of which are beyond the control of our management. In addition, the utilization forecasts with respect to our equity awards do not take into account any circumstances or events occurring after the date that they were prepared and, accordingly, do not give effect to any changes to our operations or strategy that may be implemented in the future. Accordingly, actual outcomes may be, and likely will be, materially different than those reflected in the forecasts. We disclaim any obligation to, and do not intend to, update or otherwise revise the forecasts to reflect circumstances existing after the date when made or to reflect the occurrence of future events even if any or all of the assumptions underlying the forecasts are shown to be in error. The forecasts are forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21A of the Exchange Act. These statements involve risks and uncertainties that could cause actual outcomes to differ materially from those in the forward-looking statements, including our ability to attract and retain talent, achievement of performance metrics, if any, with respect to certain equity awards, the extent of stock option exercise activity, and others described in our Annual Report on Form 10-K for the fiscal year ended December 31, 2017 filed with the Securities and Exchange Commission.

Stockholder Approval

The Restated 2007 Plan will not become effective unless this Proposal No. 3 is approved by our stockholders. If this Proposal No. 3 is approved by our stockholders, the Restated 2007 Plan will become effective upon the date of the 2018 Annual Meeting. In the event that our stockholders do not approve this Proposal No. 3, the Restated 2007 Plan will not become effective and the 2007 Plan will continue in its current form.

Stockholder approval of this Proposal No. 3 will require the affirmative vote of a majority of the votes cast in person or by proxy at the 2018 Annual Meeting.

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SUMMARY OF THE RESTATED 2007 PLAN

General

A copy of the Restated 2007 Plan is attached to this Proxy Statement as Appendix A. The following description of the Restated 2007 Plan is a summary and so is qualified by reference to the complete text of the Restated 2007 Plan. This summary reflects the terms set forth above.

The purpose of the Restated 2007 Plan is to enhance the long-term stockholder value of Seattle Genetics by offering opportunities to eligible individuals to participate in the growth in value of our equity. Stock options and stock awards, including restricted stock, restricted stock units, stock appreciation rights and similar types of awards, may be granted under the Restated 2007 Plan. Options granted under the Restated 2007 Plan may be either “incentive stock options,” as defined in Section 422 of the Code, or nonstatutory stock options.

Administration

The Restated 2007 Plan may be administered by the Board, a committee of the Board, or one or more of our officers delegated by the Board or the Board committee in accordance with the terms of the Restated 2007 Plan. We refer to the group or person that administers the Restated 2007 Plan from time to time below as the plan administrator.

Eligibility

Awards may be granted under the Restated 2007 Plan to our employees (including officers), directors and consultants and the employees, directors and consultants of our affiliates. Incentive stock options may be granted only to our employees or the employees of our subsidiaries. As of March 12, 2018, we (including our affiliates) had approximately 1122 employees, 7 non-employee directors and 37 consultants. The plan administrator selects the employees, directors and consultants to whom awards may be granted, the time or times at which such awards are granted, and the terms of such awards.

Share Reserve

If this Proposal No. 3 is approved, the total number of shares of our common stock authorized for issuance under the Restated 2007 Plan will be 33,000,000 shares, subject to adjustment for certain changes in our capitalization.

Shares subject to awards that are canceled, expired or are forfeited (including with respect to any shares that have been issued under an award) will be available for re-grant under the Restated 2007 Plan. If an awardee pays the exercise or purchase price of an award through the tendering of shares, the number of shares tendered will become available for re-grant under the Restated 2007 Plan.

Share Limits

If this Proposal No. 3 is approved, the total number of shares of our common stock that may be issued under the Restated 2007 Plan pursuant to the exercise of incentive stock options will be 66,000,000 shares, subject to adjustment for certain changes in our capitalization.

Under the Restated 2007 Plan, no awardee may be granted awards covering more than 1,000,000 shares in any calendar year, subject to adjustment for certain changes in our capitalization.

Section 162(m) Transition Relief for Performance-Based Compensation

Certain provisions in the Restated 2007 Plan refer to the “performance-based compensation” exception under Section 162(m) of the Code. Pursuant to the Tax Cuts and Jobs Act, this exception was recently repealed

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with respect to taxable years beginning after December 31, 2017. However, an award may still be eligible for this exception if, among other requirements, it is intended to qualify, and is eligible to qualify, as “performance-based compensation” under Section 162(m) of the Code pursuant to the transition relief provided by the Tax Cuts and Jobs Act for remuneration provided pursuant to a written binding contract which was in effect on November 2, 2017 and which was not modified in any material respect on or after such date. For purposes of this Proposal No. 3, the term “Section 162(m) Transition Relief” refers to such transition relief. As of the date the Board approved the Restated 2007 Plan, the U.S. Department of the Treasury and the Internal Revenue Service had not issued any applicable guidance, rulings or regulations regarding the Section 162(m) Transition Relief. Accordingly, the provisions in the Restated 2007 Plan which refer to the “performance-based compensation” exception under Section 162(m) of the Code were not removed so as not to jeopardize the ability of certain awards to qualify for the Section 162(m) Transition Relief before any such guidance, rulings or regulations are issued. However, such provisions will only apply to any award that is intended to qualify, and is eligible to qualify, as “performance-based compensation” under Section 162(m) of the Code pursuant to the Section 162(m) Transition Relief and, therefore, are not applicable to any other awards granted under the Restated 2007 Plan. Because of certain ambiguities and uncertainties as to the application and interpretation of Section 162(m) of the Code and the regulations issued thereunder, including the uncertain scope of the Section 162(m) Transition Relief, we do not know the extent to which any award granted under the Restated 2007 Plan will be eligible for the Section 162(m) Transition Relief, if at all.

Terms and Conditions of Options

Each option is evidenced by a stock option agreement between us and the optionee and is subject to the following additional terms and conditions.

Exercise Price. The plan administrator determines the exercise price of options at the time the options are granted. The exercise price of an incentive stock option or a nonstatutory stock option may not be less than 100% of the fair market value of our common stock on the date the option is granted, provided that the exercise price of an incentive stock option granted to an employee who holds more than 10% of the voting power of all classes of our stock may not be less than 110% of the fair market value of our common stock on the date the option is granted. However, we may grant options with exercise prices less than the fair market value of our common stock on the date of grant in connection with an acquisition by us of another company. The fair market value of our common stock is the closing price for the shares as reported on the Nasdaq Global Select Market as of the applicable date. As of March 22, 2018, the closing price of our common stock as reported on the Nasdaq Global Select Market was $53.21 per share.

Exercise of Option; Form of Consideration. The plan administrator determines when options vest and become exercisable and in its discretion may accelerate the vesting of any outstanding option; provided, however, that (i) each option must have a minimum vesting period of one year from the earlier of the date of grant or vesting commencement date, if any, and (ii) in the event of an optionee’s termination due to death or disability, the vesting and exercisability of each outstanding time-based option granted to the optionee under the Restated 2007 Plan will be accelerated for an additional 12 months. The means of payment for shares issued upon exercise of an option are specified in each option agreement. The Restated 2007 Plan permits payment to be made by cash, check, wire transfer, other shares of our common stock (with some restrictions), broker assisted same-day sales, cashless “net exercise” arrangements, any other form of consideration permitted by applicable law and the plan administrator, or any combination thereof.

Term of Option. The term of an option may be no more than ten years from the date of grant, provided that the term of an incentive stock option granted to an employee who holds more than 10% of the voting power of all classes of our stock may be no more than five years from the date of grant. No option may be exercised after the expiration of its term.

Termination of Service. If an optionee’s service as an employee, director or consultant (referred to in this Proposal No. 3 as “service”) terminates for any reason other than cause, death or disability, then options held by

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the optionee under the Restated 2007 Plan generally will be exercisable to the extent they are vested and exercisable on the termination date for a period (as specified by the plan administrator) after the termination date but not after the options’ expiration date. If an optionee’s service terminates for cause, then the plan administrator has the authority to terminate all options held by the optionee under the Restated 2007 Plan immediately.

Generally, if an optionee’s service terminates as a result of the optionee’s death or in the event of an optionee’s death within 30 days following the optionee’s termination of service, all outstanding options that were vested and exercisable as of the date of the optionee’s death may be exercised for twelve months following the optionee’s death but in no event after the options’ expiration date. Generally, if an optionee’s service terminates as a result of the optionee’s disability, then all options to the extent they are vested and exercisable on the termination date may be exercised for twelve months following the termination date but in no event after the options’ expiration date. The plan administrator has the authority to extend the period of time for which an option is to remain exercisable following an optionee’s termination (taking into account limitations and consequences under the Code) but not beyond the expiration of the term of the option.

Terms and Conditions of Stock Awards

Stock awards may be restricted stock grants, restricted stock units, stock appreciation rights or other similar awards. Restricted stock grants are awards of a specific number of shares of our common stock. Restricted stock units represent a promise to deliver shares of our common stock, or an amount of cash or property equal to the value of the underlying shares, at a future date. Stock appreciation rights are rights to receive cash and/or shares of our common stock based on the amount by which the exercise date fair market value of a specific number of shares exceeds the grant date fair market value of the exercised portion of the stock appreciation right.

Each stock award agreement will contain provisions regarding (i) the number of shares subject to the stock award, (ii) the purchase price of the shares, if any, and the means of payment for the shares, (iii) the performance criteria (including qualifying performance criteria), if any, and level of achievement versus these criteria that will determine the number of shares granted, issued, retainable and vested, as applicable, (iv) such terms and conditions on the grant, issuance, vesting, settlement, and forfeiture of the shares, as applicable, as may be determined from time to time by the plan administrator, (v) restrictions on the transferability of the stock award, and (vi) such further terms and conditions, in each case not inconsistent with the Restated 2007 Plan, as may be determined from time to time by the plan administrator; provided, however, that (i) each stock award must have a minimum vesting period of one year from the earlier of the date of grant or the vesting commencement date, if any, and (ii) in the event of an awardee’s termination due to death or disability, the vesting (and exercisability, if applicable) of each outstanding time-based stock award granted to the awardee under the Restated 2007 Plan will be accelerated for an additional 12 months.

Repricing; Cancellation and Re-Grant of Awards

No option or stock appreciation right may be repriced to reduce the exercise or strike price of such option or stock appreciation right without stockholder approval (except in connection with a change in our capitalization—see “Adjustments upon Changes in Capitalization, Change in Control or Dissolution” below). Additionally, the plan administrator will not have the authority to cancel any outstanding option or stock appreciation right that has an exercise or strike price greater than the then-current fair market value of our common stock in exchange for cash or other awards under the Restated 2007 Plan, unless our stockholders have approved such an action within twelve months prior to such an event.

Nontransferability

Generally, awards granted under the Restated 2007 Plan are not transferable other than by will or the laws of descent and distribution or to a designated beneficiary upon the awardee’s death. The plan administrator may in

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its discretion make an award transferable to an awardee’s family member or any other person or entity as it deems appropriate.

Qualifying Performance Criteria

The Restated 2007 Plan permits us to grant awards incorporating performance objectives called “qualifying performance criteria”. Qualifying performance criteria means any one or more of the performance criteria listed below, either individually, alternatively or in combination, applied to either Seattle Genetics as a whole or to a business unit, affiliate or business segment, either individually, alternatively or in any combination, and measured either annually or cumulatively over a period of years, on an absolute basis or relative to a pre-established target, to previous years’ results or to a designated comparison group, in each case as specified by the plan administrator in the award agreement: (i) cash flow; (ii) earnings (including gross margin, earnings before interest and taxes, earnings before taxes, and net earnings); (iii) earnings per share; (iv) growth in earnings or earnings per share; (v) stock price; (vi) return on equity or average stockholders’ equity; (vii) total stockholder return; (viii) return on capital; (ix) return on assets or net assets; (x) return on investment; (xi) revenue; (xii) income or net income; (xiii) operating income or net operating income, in aggregate or per share; (xiv) operating profit or net operating profit; (xv) operating margin; (xvi) return on operating revenue; (xvii) market share; (xviii) growth in stockholder value relative to the moving average of a peer group index; (xix) strategic plan development and implementation (including individual performance objectives that relate to achievement of Seattle Genetics or any business unit’s strategic plan); (xx) improvement in workforce diversity; (xxi) growth of revenue, operating income or net income; (xxii) approval by the U.S. Food and Drug Administration or other regulatory body of a product candidate; and (xxiii) any other similar criteria.

The Compensation Committee may appropriately adjust any evaluation of performance under a qualifying performance criteria to exclude any of the following events that occurs during a performance period: (A) asset write-downs; (B) litigation or claim judgments or settlements; (C) the effect of changes in tax law, accounting principles or other such laws or provisions affecting reported results; (D) accruals for reorganization and restructuring programs and/or other nonrecurring charges; and (E) any gains or losses that are “unusual” in nature or occur “infrequently” under generally accepted accounting principles or discontinued operations in our financial statements.

Deferral of Award Benefits

The plan administrator may permit awardees whom it selects to defer compensation payable pursuant to the terms of an award or defer compensation arising outside the terms of the Restated 2007 Plan pursuant to a program that provides for deferred payment in satisfaction of other compensation amounts through the issuance of one or more awards under the Restated 2007 Plan and in a manner that complies with Section 409A of the Code.

Adjustments upon Changes in Capitalization, Change in Control or Dissolution

In the event of any stock split, reverse stock split, combination or reclassification of common stock, stock dividend, spin-off, or similar change to our capital structure effected without receipt of consideration by us, the plan administrator will make proportionate adjustments to (i) the number and kind of shares covered by each outstanding award under the Restated 2007 Plan, (ii) the exercise or purchase (including repurchase) price per share subject to each outstanding award under the Restated 2007 Plan and (iii) each of the share limitations under the Restated 2007 Plan.

In the event of (i) an acquisition of us by means of any transaction or series of related transactions, including any reorganization, merger or consolidation but excluding any merger effected exclusively for the purpose of changing our domicile, (ii) any sale of all or substantially all of our assets or (iii) any other event specified by the plan administrator, so long as in either (i) or (ii), our stockholders of record immediately prior to the transaction

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hold less than 50% of the voting power of the surviving entity and, so long as in (iii) that no change in control will be deemed to occur upon announcement or commencement of a tender offer or upon a “potential” takeover or upon stockholder approval of a merger or other transaction, in each case without a requirement that the change in control actually occur (each, a “change in control”), then:

In the event of a liquidation or dissolution, any options or stock awards that have not been exercised will terminate immediately prior to the transaction.

The plan administrator has the authority to accelerate vesting of outstanding awards under the Restated 2007 Plan at any time in its sole discretion.

Amendment and Termination of the Restated 2007 Plan

The plan administrator may amend, alter or discontinue the Restated 2007 Plan or any award agreement at any time. However, we will obtain stockholder approval for any amendment to the Restated 2007 Plan if stockholder approval is necessary or desirable to comply with any applicable law or listing requirements. In addition, we will obtain stockholder approval of any of the following: (i) an increase to the shares reserved for issuance under the Restated 2007 Plan other than an increase in connection with a change in our capitalization as described in “Adjustments upon Changes in Capitalization, Change in Control or Dissolution” above; (ii) a change of the class of persons eligible to receive awards under the Restated 2007 Plan; (iii) a reduction in the minimum exercise prices at which options or stock appreciation rights may be granted; or (iv) any amendment of outstanding options or stock appreciation rights that results in a repricing of such awards. No amendment of the Restated 2007 Plan will impair the rights of an outstanding award without the consent of the awardee, except as otherwise provided in the Restated 2007 Plan. If the Restated 2007 Plan is approved by our stockholders, then unless sooner terminated, the Restated 2007 Plan will automatically terminate on May 18, 2028, which is the date ten years from the date of stockholder approval of the Restated 2007 Plan.

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Restated 2007 New Plan Benefits

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2007 Plan Benefits

The following table sets forth, for each of the individuals and the various groups indicated, the total number of shares of our common stock subject to awards that have been granted (even if not currently outstanding) under the 2007 Plan since its approval by our stockholders in 2007 through March 12, 2018.

EQUITY COMPENSATION PLAN INFORMATION

Please see the section of this proxy statement entitled “Equity Compensation Plan Information” for certain information with respect to compensation plans under which equity securities of Seattle Genetics are authorized for issuance.

FEDERAL INCOME TAX CONSEQUENCES

THE FOLLOWING IS A GENERAL SUMMARY OF THE FEDERAL INCOME TAX CONSEQUENCES OF THE ISSUANCE AND EXERCISE OF OPTIONS OR OTHER AWARDS UNDER THE RESTATED 2007 PLAN. IT DOES NOT DESCRIBE STATE OR OTHER TAX CONSEQUENCES OF THE ISSUANCE AND EXERCISE OF OPTIONS OR OTHER AWARDS. THE INFORMATION SET FORTH BELOW IS A SUMMARY ONLY AND DOES NOT PURPORT TO BE COMPLETE. THE INFORMATION IS BASED UPON CURRENT FEDERAL INCOME TAX RULES AND THEREFORE IS SUBJECT TO CHANGE WHEN THOSE RULES CHANGE. THE RESTATED 2007 PLAN IS NOT QUALIFIED UNDER THE PROVISIONS OF SECTION 401(A) OF THE CODE AND IS NOT SUBJECT TO ANY OF THE PROVISIONS OF THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974. OUR ABILITY TO REALIZE THE BENEFIT OF ANY TAX DEDUCTIONS DESCRIBED BELOW DEPENDS ON OUR GENERATION OF TAXABLE INCOME, AS WELL AS THE REQUIREMENT OF REASONABLENESS,

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THE PROVISIONS OF SECTION 162(M) OF THE CODE AND THE SATISFACTION OF OUR TAX REPORTING OBLIGATIONS.

Options

The grant of an incentive stock option has no federal income tax effect on the optionee. Upon exercise the optionee does not recognize income for “regular” tax purposes. However, the excess of the fair market value of the stock subject to an option over the exercise price of such option (which is often referred to as the “option spread”) is included in the optionee’s “alternative minimum taxable income” for purposes of the alternative minimum tax. If the optionee does not dispose of the stock acquired upon exercise of an incentive stock option until more than two years after the option grant date and more than one year after exercise of the option, any gain (or loss) upon sale of the shares will be a long-term capital gain (or loss). If shares are sold or otherwise disposed of before these periods have expired, which is referred to as a disqualifying disposition, the option spread at the time of exercise of the option (but not more than the amount of the gain on the sale or other disposition) is ordinary income in the year of such sale or other disposition. If gain on a disqualifying disposition exceeds the amount treated as ordinary income, the excess is taxable as capital gain (which will be long-term capital gain if the shares have been held more than one year after the date of exercise of the option). We are not entitled to a federal income tax deduction in connection with incentive stock options, except to the extent that the optionee has taxable ordinary income on a disqualifying disposition (unless limited by Section 162(m)).

The grant of a nonstatutory stock option having an exercise price equal to the grant date fair market value of our common stock has no federal income tax effect on the optionee. Upon the exercise of a nonstatutory stock option, the optionee has taxable ordinary income (and unless limited by Section 162(m), we are entitled to a corresponding deduction) equal to the option spread on the date of exercise. Upon the disposition of stock acquired upon exercise of a nonstatutory stock option, the optionee recognizes either long-term or short-term capital gain or loss, depending on how long such stock was held, on any difference between the sale price and the exercise price, to the extent not recognized as taxable income on the date of exercise. We may allow nonstatutory stock options to be transferred subject to conditions and restrictions imposed by the plan administrator; special tax rules may apply on such a transfer. In the case of both incentive stock options and nonstatutory stock options, special federal income tax rules apply if our common stock is used to pay all or part of the option price, and different rules than those described above will apply if unvested shares are purchased on exercise of the option.

Stock Awards

Stock Awards. Stock awards will generally be taxed in the same manner as nonstatutory stock options. Shares issued under a restricted stock award are subject to a “substantial risk of forfeiture” within the meaning of Section 83 of the Code to the extent the shares will be forfeited in the event that the participant ceases to provide services to us and are not transferable. As a result of this substantial risk of forfeiture, the participant will not recognize ordinary income at the time the award shares are issued. Instead, the participant will recognize ordinary income on the dates when the stock is no longer subject to a substantial risk of forfeiture, or when the stock becomes transferable, if earlier. The participant’s ordinary income is measured as the difference between the amount paid for the stock, if any, and the fair market value of the stock on the date the stock is no longer subject to forfeiture.

The participant may accelerate his or her recognition of ordinary income, if any, and begin his or her capital gains holding period by timely filing (i.e., within thirty days of the share issuance date) an election pursuant to Section 83(b) of the Code. In such event, the ordinary income recognized, if any, is measured as the difference between the amount paid for the stock, if any, and the fair market value of the stock on the date of such issuance, and the capital gain holding period commences on such date. The ordinary income recognized by an employee will be subject to tax withholding by us. We are entitled to a deduction in the same amount as and at the time the employee recognizes ordinary income.

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Stock Appreciation Rights. We may grant under the Restated 2007 Plan stock appreciation rights separate from any other award or in tandem with other awards under the Restated 2007 Plan. Where the stock appreciation rights are granted with a strike price equal to the fair market value of the underlying stock on the grant date, the participant will recognize ordinary income equal to the fair market value of the stock or cash received upon such exercise. Subject to the requirement of reasonableness, the provisions of Section 162(m) of the Code, and the satisfaction of a tax reporting obligation, we will generally be entitled to a tax deduction equal to the taxable ordinary income realized by the participant in connection with the stock appreciation right.

Restricted Stock Units. Generally, the recipient of a stock unit structured to conform to the requirements of Section 409A of the Code or an exception to Section 409A of the Code will recognize ordinary income at the time the stock is delivered equal to the excess, if any, of the fair market value of the shares of our common stock received over any amount paid by the participant in exchange for the shares of our common stock. To conform to the requirements of Section 409A of the Code, the shares of our common stock subject to a stock unit award may generally only be delivered upon one of the following events: a fixed calendar date (or dates), separation from service, death, disability or a change in control. If delivery occurs on another date, unless the stock units otherwise comply with or qualify for an exception to the requirements of Section 409A of the Code, in addition to the tax treatment described above, the participant will owe an additional 20% federal tax and interest on any taxes owed.

The participant’s basis for the determination of gain or loss upon the subsequent disposition of shares acquired from stock units, will be the amount paid for such shares plus any ordinary income recognized when the stock is delivered.

Subject to the requirement of reasonableness, the provisions of Section 162(m) of the Code and the satisfaction of a tax reporting obligation, we will generally be entitled to a tax deduction equal to the taxable ordinary income realized by the participant.

Section 409A of the Code

The American Jobs Creation Act of 2004 added Section 409A to the Code, generally effective January 1, 2005. Section 409A covers most programs that defer the receipt of compensation to a succeeding year. It provides rules for elections to defer, if any, and for timing of payouts. There are significant penalties placed on the individual participant for failure to comply with Section 409A. However, it does not impact our ability to deduct deferred compensation.

Section 409A does not apply to incentive stock options, nonstatutory stock options that have an exercise price that is at least equal to the grant date fair market value and restricted stock provided there is no deferral of income beyond the vesting date. Section 409A also does not cover stock appreciation rights if the exercise price is not less than the fair market value of the underlying stock on the date of grant, the rights are settled in such stock and no features defer the recognition of income beyond the exercise date.

Section 162(m) of the Code

Section 162(m) of the Code disallows a deduction to any publicly held corporation and its affiliates for certain compensation paid to “covered employees” in a taxable year to the extent that compensation to a covered employee exceeds $1 million. Prior to the recent enactment of the Tax Cuts and Jobs Act, compensation that qualified as “performance-based compensation” under Section 162(m) of the Code was not subject to this deduction limitation. Pursuant to the Tax Cuts and Jobs Act, this exception for “performance-based compensation” under Section 162(m) of the Code was repealed with respect to taxable years beginning after December 31, 2017, except that certain transition relief is provided by the Tax Cuts and Jobs Act for remuneration provided pursuant to a written binding contract which was in effect on November 2, 2017 and which was not modified in any material respect on or after such date. As a result, compensation paid to any of

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our “covered employees” in excess of $1 million per taxable year generally will not be deductible unless, among other requirements, it is intended to qualify, and is eligible to qualify, as “performance-based compensation” under Section 162(m) of the Code pursuant to the transition relief provided by the Tax Cuts and Jobs Act. Because of certain ambiguities and uncertainties as to the application and interpretation of Section 162(m) of the Code and the regulations issued thereunder, including the uncertain scope of the transition relief provided by the Tax Cuts and Jobs Act, no assurance can be given that any award granted under the Restated 2007 Plan will be eligible for such transition relief and, therefore, eligible for the “performance-based compensation” exception under Section 162(m) of the Code.

ACCOUNTING TREATMENT

We will recognize compensation cost in connection with awards granted under the Restated 2007 Plan as required under applicable accounting standards. We currently amortize compensation cost associated with equity awards over an award’s requisite service period and establish fair value of equity awards in accordance with applicable accounting standards.

THE BOARD RECOMMENDS A VOTE FOR THIS PROPOSAL NO. 3

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PROPOSAL NO. 4

ADVISORY VOTE ON EXECUTIVE COMPENSATION

Under the Dodd-Frank Wall Street Reform and Consumer Protection Act (the “Dodd-Frank Act”) and Section 14A of the Exchange Act, our stockholders are entitled to vote to approve, on an advisory (non-binding) basis, the compensation of our Chief Executive Officer, Chief Financial Officer and our three other most highly compensated executive officers during the year ended December 31, 2017 (collectively, the “Named Executive Officers”) as disclosed in this proxy statement in accordance with the SEC’s rules. This non-binding advisory vote is commonly referred to as a “say-on-pay” vote.

At last year’s annual meeting, we provided our stockholders with the opportunity to cast an advisory vote regarding the compensation of our named executive officers as disclosed in the proxy statement for the 2017 Annual Meeting of Stockholders. At the 2017 Annual Meeting of Stockholders, our stockholders overwhelmingly approved the proposal, with approximately 98% of the votes cast voting in favor of the proposal. This year we are again asking our stockholders to vote “FOR” the compensation of our Named Executive Officers as disclosed in this proxy statement in accordance with the SEC’s rules.

As described in detail under the heading “Compensation of Executive Officers—Compensation Discussion and Analysis,” our executive compensation programs are designed to retain and incentivize the high quality executives whose efforts are key to our long-term success. Under these programs, our Named Executive Officers are rewarded on the basis of individual and corporate performance measured against pre-established corporate and strategic goals. Please read the section of this proxy statement under the heading “Compensation of Executive Officers—Compensation Discussion and Analysis” for additional details about our executive compensation programs, including information about the 2017 compensation of our Named Executive Officers.

The Compensation Committee of our Board of Directors continually reviews the compensation programs for our Named Executive Officers to ensure they achieve the desired goals of aligning our executive compensation structure with our stockholders’ interests and current market practices.

We are asking our stockholders to indicate their support for our Named Executive Officer compensation as described in this proxy statement. This proposal gives our stockholders the opportunity to express their views on our Named Executive Officers’ compensation. This vote is not intended to address any specific item of compensation, but rather the overall compensation of our Named Executive Officers and the philosophy, policies and practices described in this proxy statement. Accordingly, we are asking our stockholders to cast a non-binding advisory vote “FOR” the following resolution at the Annual Meeting:

“RESOLVED, that the compensation paid to the Named Executive Officers, as disclosed in the Company’s Proxy Statement for the 2018 Annual Meeting of Stockholders pursuant to Item 402 of Regulation S-K, including the Compensation Discussion and Analysis, compensation tables and narrative discussion is hereby APPROVED.”

The say-on-pay vote is advisory, and therefore not binding on Seattle Genetics, the Compensation Committee or our Board of Directors. Nevertheless, our Board of Directors and our Compensation Committee value the opinions of our stockholders, whether expressed through this vote or otherwise and, accordingly, the Board and Compensation Committee intend to consider the results of this vote in making determinations in the future regarding executive compensation arrangements.

Unless our Board of Directors modifies its policy on the frequency of future advisory votes on the compensation of our named executive officers, the next advisory vote on the compensation of our named executive officers will be held at the 2019 Annual Meeting of Stockholders. In addition, our stockholders will be able to indicate by advisory vote at our 2023 Annual Meeting of Stockholders their preference as to the frequency of future advisory votes.

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Stockholder approval of this Proposal No. 4 will require the affirmative vote of a majority of the votes cast in person or by proxy at the Annual Meeting.

THE BOARD RECOMMENDS A VOTE FOR THIS PROPOSAL NO. 4

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COMPENSATION OF EXECUTIVE OFFICERS

COMPENSATION DISCUSSION AND ANALYSIS

Our compensation discussion and analysis discusses and analyzes how the Compensation Committee of our Board of Directors (the “Compensation Committee”) determined the total compensation for our Chief Executive Officer, Chief Financial Officer, our three other most highly compensated executive officers during the year ended December 31, 2017 serving as of December 31, 2017, and one former executive officer who departed from the Company during 2017 but whose total compensation for 2017 would have made him one of the three most highly compensated executive officers for 2017, who were:

We refer to these executive officers as our “Named Executive Officers” or our “named executive officers”.

Our compensation discussion and analysis describes our overall executive compensation philosophy, objectives and practices, as well as the Compensation Committee’s decisions and determinations regarding executive compensation for 2017.

Executive Summary

2017 Business Highlights

The financial and operational highlights of our company performance for 2017 were as follows:

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2017 Executive Compensation Highlights

The following key compensation actions were taken with respect to the Named Executive Officers for 2017:

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Executive Compensation Policies and Practices

We endeavor to maintain sound executive compensation policies and practices, including compensation-related corporate governance standards, consistent with our executive compensation philosophy. During 2017, we maintained the following executive compensation policies and practices to drive performance and to minimize behaviors that we believe do not serve our stockholders’ long-term interests:

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Results of Most Recent Stockholder Advisory Vote on Executive Compensation

Approximately 99% of the votes cast in the “say-on-pay” stockholder advisory vote on the compensation of our Named Executive Officers in 2017 approved our executive compensation as described in our 2017 definitive proxy statement. The Compensation Committee considered the result of the stockholder advisory vote as an endorsement of its compensation policies, practices and philosophy for our Named Executive Officers. Accordingly, the Compensation Committee determined not to make any significant changes as a result of the vote. In addition, in part based on the support shown by the vote, the Compensation Committee has maintained a consistent approach in making compensation decisions.

The Compensation Committee considers the results of the say-on-pay vote on our executive compensation program as part of its annual executive compensation review. Our Board of Directors values the opinions of our stockholders, and the Compensation Committee will continue to consider the outcome of future say-on-pay votes, as well as any feedback received throughout the year, when making compensation decisions for the Named Executive Officers. The next say-on-pay vote on the compensation of the Named Executive Officers will take place at the Annual Meeting.

Compensation Philosophy and Objectives

Our compensation philosophy is to provide overall compensation that is competitive to attract and retain the highest caliber executive officers. In particular, we believe that, when targeted levels of performance are achieved, the resulting compensation should approximate the 50^th percentile of pay practices of a peer group of companies selected by the Compensation Committee, and that additional performance should be rewarded by adjusting compensation upwards towards the 75^th percentile of our peer group if an individual’s and our corporate performance exceeds expectations. The Compensation Committee believes that this approach is reasonable and appropriate to achieve the objectives of our compensation program and applies its experience and judgment when interpreting competitive market data and making compensation decisions for our executive officers. Other key objectives of our executive compensation program include aligning pay with company performance, driving the achievement of key business goals that increase stockholder value over the long-term and weighting pay deliberately toward “at risk” performance-based compensation.

Compensation-Setting Process

Role of the Compensation Committee

The Compensation Committee’s basic responsibility is to review the performance of our management in achieving corporate goals and objectives and to ensure that our management is compensated effectively in a manner consistent with our compensation philosophy, competitive practice and the requirements of the appropriate regulatory bodies. Toward that end, the Compensation Committee oversees, reviews, and approves our executive compensation program.

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For 2017, the Compensation Committee reviewed the base salaries, annual cash incentive compensation opportunities, and the long-term incentive compensation of our Named Executive Officers and compared them to our compensation peer group as described below in “—Competitive Positioning” primarily to ensure that our Named Executive Officer target total direct compensation opportunities as a whole were market competitive and to determine whether any adjustments were necessary. Generally, the Compensation Committee seeks to establish a mix between cash compensation and long-term equity incentives similar to the mix used by the companies in our compensation peer group. For example, generally, and for 2017, the Compensation Committee set a significant portion of compensation to be “at risk” based on our performance, in the form of both cash and equity, with heavier weight towards equity incentives that directly align the interests of our executives with our stockholders. The Compensation Committee believes that it is important to align compensation levels and the mix of compensation to that offered by our peers in order to retain and incentivize the talented executive officers whose efforts are key to our long-term success.

At the time it makes its executive compensation decisions, the Compensation Committee also reviews individual performance and the Company’s performance against pre-established company corporate and strategic goals, as well as the Company’s performance generally. In this regard, decisions with respect to the principal, ongoing elements of compensation for our executive officers are based, in combination with the competitive market analysis described above, upon the Compensation Committee’s assessment of:

Generally, determinations of individual performance at the executive officer level are based on a holistic evaluation of the executive’s performance taking into account department and functional goals which are aligned with the broader corporate and strategic goals of the company. The Compensation Committee believes that successful execution against these goals is an essential way to enhance long-term stockholder value. The executive officer’s role and responsibilities and job criticality are also considered.

The Compensation Committee generally relies upon its judgment and not upon rigid guidelines or formulas in determining the amount and mix of compensation elements for each executive officer, particularly with respect to base salary determinations and overall levels of long-term incentive compensation. However, as set forth below, bonus awards under our Executive Bonus Plan are formulaic in that the target and maximum bonus opportunities are established, as is the extent to which bonuses are awarded based on the achievement of pre-established company goals and, in the case of our Named Executive Officers other than our CEO, on individual performance. In addition, since 2011 for reasons described further below in “—Principal Elements of Compensation—Long Term Equity Awards,” the Compensation Committee has delivered annual stock awards in a combination of options to purchase shares of our common stock and RSU awards that may be settled for shares of our common stock, with options representing approximately 50% of the overall value of the equity awards granted and with RSU awards comprising the other approximately 50%. Specifically, a stock option equivalent value is determined for each executive officer role after the Compensation Committee reviews peer group data. This total value is then divided in half, and approximately 50% of the value as of the calculation date shortly preceding the applicable grant date is allocated to be granted in the form of options and approximately 50% of the value is allocated to be granted in the form of RSUs. In each case, the shares are determined based on an approximation of grant date fair value, using the Black Scholes methodology for stock options and a 0.4 multiplier for RSUs (to reflect the increased value of receiving shares at full value without the payment of an exercise price). This 50/50 mix is based on the goal of attracting and retaining top performers and reflects a balanced approach between options, a more leveraged equity instrument that helps to drive stockholder value, and RSU awards, that serve as an effective retention vehicle even in periods of volatility.

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Role of Executive Officers

Our CEO makes recommendations to the Compensation Committee with respect to base salary levels, target annual cash incentive award opportunities, individual performance assessments, and the amount of long-term equity awards to be granted to our executive officers (other than with respect to his own compensation) in consultation with Compensia and our Executive Vice President, Human Resources. In addition, our Executive Vice President, Human Resources supports the Compensation Committee in its work, including preparation of historical and prospective executive compensation data, review of peer group data and biotechnology market practices, and research in response to technical Compensation Committee inquiries. Other than as described above, neither the CEO nor any other executive officers take part in the Compensation Committee’s decisions regarding executive officer compensation.

Role of Compensation Consultant

Under its charter, the Compensation Committee has the authority, in its sole discretion, to retain (or obtain the advice of) any compensation consultant, legal counsel or other adviser to assist it in the performance of its duties and responsibilities. Pursuant to this authority, the Compensation Committee has engaged Compensia, Inc., a national compensation consulting firm, for support on matters related to the compensation of our executive officers. The Compensation Committee has retained Compensia since it has found Compensia’s work to be thorough and objective.

In 2017, the Compensation Committee analyzed whether the work of Compensia as a compensation consultant has raised any conflict of interest, taking into consideration the following factors: (i) the provision of other services to our company by Compensia; (ii) the amount of fees from our company paid to Compensia as a percentage of the firm’s total revenue; (iii) Compensia’s policies and procedures that are designed to prevent conflicts of interest; (iv) any business or personal relationship of Compensia or the individual compensation advisors employed by the firm with an executive officer of our company; (v) any business or personal relationship of the individual compensation advisors with any member of the Compensation Committee; and (vi) any stock of the Company owned by the individual compensation advisors employed by the firm. The Compensation Committee determined, based on its analysis of the above factors, that the work of Compensia and the individual compensation advisors employed by Compensia as compensation consultants to our company has not created any conflict of interest.

Base salary and annual target bonus decisions made in January 2017 were made after considering the compensation provided by our peer group and Compensia’s previously provided competitive market analysis with respect to our January 2016 peer group. The base salary data considered by the Compensation Committee in making the January 2017 base salary decisions were aged by applying an annualized 3% increase to the January 2016 peer group data. Compensia was again retained by the Compensation Committee in August 2017 to provide an updated competitive market analysis of the base salary, annual cash incentive awards, and long-term incentive compensation of our executive officers compared against our compensation peer group and to review other market practices and trends. This market analysis was reviewed with the Compensation Committee and was used to guide decisions regarding the August 2017 grants of long term equity awards in the form of options and RSUs. These data were also used to determine salary and cash incentive targets in January 2018.

Competitive Positioning

The Compensation Committee reviews our peer group periodically to reflect changes in market capitalization and other factors, including acquisitions, and revises the companies included in the peer group accordingly.

The peer group used by the Compensation Committee when making salary and bonus target compensation decisions in January 2017 was our peer group that resulted from Compensia’s analysis in January 2016 that was

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approved by the Compensation Committee, with input provided by senior management and Compensia at that time, and consisted of:

The compensation peer group used by the Compensation Committee to review compensation in August 2017 was approved by the Compensation Committee, with input provided by senior management and Compensia, and included biotechnology and pharmaceutical companies that were similar to the Company with respect to revenue, market capitalization, headcount, development and commercialization stage and product and innovation focus. In each case, as of the date this analysis was performed, these twenty peer companies had a median market capitalization of approximately $6.8 billion, as compared to our market capitalization of approximately $9 billion, median 12-month revenue through June 30, 2017 of approximately $89 million, as compared to our 12-month revenue through June 30, 2017 of approximately $429 million, and a median of 456 employees, as compared to our 890 employees. This peer group consisted of:

Principal Elements of Compensation

Our executive compensation program currently consists of four principal components: base salary, annual cash incentive awards (if approved by the Compensation Committee), long-term equity awards, currently in the form of stock options and RSU awards which are subject to time-based vesting, and performance-based incentive awards. The Compensation Committee seeks to ensure the aggregate level of pay across all of the pay elements (base, total cash, annual, long-term incentives and performance-based incentives) is meeting our desired compensation objectives for each executive officer.

Base Salary

We use base salaries to attract and retain talented executives. The Compensation Committee establishes the base salaries for our CEO and other executive officers based on the underlying scope of their respective responsibilities, after taking into account competitive market compensation by reviewing the base salaries paid by our peer group for similar positions. The base salary for each executive officer is initially determined on an annual basis by first referencing the 50^th percentile for similarly positioned executives based on the peer group data, and then by adjusting for other factors, including individual performance, changes in job duties and

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responsibilities, compensation relative to our other executive officers, budget considerations, scope and criticality of role, and other factors as applicable. Typically, annual base salary adjustments are effective February 1 of each year.

Annual Cash Incentive Awards

We have adopted an Executive Bonus Plan, which provides cash incentives designed to reward each executive officer for our corporate performance and such officer’s individual contributions and performance toward achieving key corporate goals. The performance metrics against which our executive officers are measured are clearly communicated, measureable and consistently applied. The corporate goals are generally approved by the Compensation Committee near the beginning of each year, but the Compensation Committee reserves the right to modify these goals to reflect changing business circumstances.

In making its assessment regarding the extent to which the corporate performance objectives for the year have been achieved, the Compensation Committee considers both the extent to which the objectives have been achieved or exceeded as well as the difficulty of each objective that was achieved compared to any objectives that were not achieved and any significant additional achievements that were not contemplated at the beginning of the performance year. The Compensation Committee also assesses performance on an overall basis. The corporate payout factor determined by this process is then used to calculate the corporate portion of each executive officer’s annual bonus payout.

Our CEO assesses the other executive officers’ contributions to the corporate goals, and makes a recommendation to the Compensation Committee with respect to the individual performance percentage. The factors considered by the CEO in making this determination include a holistic evaluation of performance, the criticality of the executive officer’s role in achieving corporate deliverables, the executive officer’s contribution to achieving corporate goals and the achievement of individual or departmental goals. The Compensation Committee reviews the CEO’s recommendations on individual performance factors for each executive officer and then makes a final determination of the individual performance percentage for each executive officer. No individual performance factor is determined for the CEO since his annual cash incentive award is based entirely on the corporate performance factor discussed above.

The weighting between the corporate performance percentage and the individual performance percentage used for determining the annual cash incentive awards is determined for each executive officer based on his or her position is as set forth in the table below. The Compensation Committee determined that greater weighting of the corporate goals should apply to our CEO and our former Chief Operating Officer than our other Named Executive Officers because their positions and responsibilities give them more opportunity to significantly impact overall corporate performance. With respect to Dr. Siegall, the corporate performance percentage is 100% and the individual performance percentage is 0%, with respect to Mr. Dobmeier, the corporate performance percentage was 80% and the individual performance percentage was 20%, and with respect to each of Mr. Simpson, Dr. Drachman, Dr. Himes and Ms. Liu, the corporate performance percentage is 60% and the individual performance percentage is 40%.

The target annual cash incentive award opportunity (expressed as a percentage of base salary) for each executive officer is determined by the Compensation Committee after referencing the bonus targets for similarly positioned executives in our peer group.

The corporate performance percentage and individual performance percentage (weighted as described above) are then multiplied by the target annual cash incentive award opportunity (expressed as a percentage of base salary) for each executive officer to determine the actual amount of the bonus award.

Corporate and individual performance goal achievement is targeted at 100%.The achieved corporate performance percentage and/or the achieved individual performance percentage may exceed 100% in the event

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we and/or the executive officer exceed expected goals, provided that neither percentage may exceed 150%. Accordingly, each executive officer’s target annual cash incentive award opportunity under the Executive Bonus Plan is capped at 150% of the target bonus amount, and in addition, each executive officer must achieve at least a 50% individual performance percentage to receive a bonus award under the Executive Bonus Plan (other than our CEO whose annual cash incentive award is based solely on the achievement of our corporate goals).

Long-Term Equity Awards

We offer long-term incentive compensation in the form of equity awards to our executive officers to align their incentives with stockholder value creation. Generally, a significant equity award is granted at the time an executive officer commences employment. Thereafter, equity awards may be granted at varying times and in varying amounts in the discretion of the Compensation Committee, but are generally granted once a year unless such executive officer is promoted, provided with a retention grant, or recognized for outstanding performance or in the case of performance-based incentive awards.

The equity awards granted to our executive officers include options to purchase shares of our common stock and RSU awards that may be settled for shares of our common stock. The Compensation Committee believes that, while both stock options and RSU awards enable our executive officers to benefit, like stockholders, from any increases in the value of our common stock, stock options deliver future value only if the value of our common stock increases above the exercise price and thereby provide incentives for our executive officers to increase the value of our common stock over the long term. Because stock options generally vest over four years, they also provide a long-term retention incentive. The Compensation Committee grants RSU awards because they are less dilutive to our stockholders, as fewer shares of our common stock are granted to achieve an equivalent value relative to stock options, and because, relative to options, RSUs are an effective retention tool even in a case in which our trading price is low as compared with option exercise prices. Generally, each RSU award granted vests in full on the third-anniversary of the date of grant, subject to continued service, so that the awards are designed to provide a long-term retention incentive.

Generally, the value of proposed annual equity awards for each named executive officer are determined first by referencing the 50^th percentile of the compensation peer group and then adjusted based on individual performance, contributions to corporate and strategic goals, consideration of the retention value of the executive officer’s total equity holdings, and an assessment of the scale and business criticality of the executive’s role.

The options to purchase shares of our common stock granted to our Named Executive Officers generally vest as to 25% of the shares on the first anniversary of the grant date and as to 1/36th of the remaining shares each month thereafter until such grant is fully vested on the fourth anniversary of the grant date. Such options are also subject to vesting acceleration as described under “—Post-Employment Compensation” below.

Generally, upon hiring an executive officer, an equity award will be granted on the fifteenth day of the month following the month he or she commences employment (or first business day thereafter). Annual equity awards to all executive officers are granted at regularly scheduled meetings of the Compensation Committee and are generally made in August. We do not have any program, plan or practice to time stock awards to our executive officers or other employees in coordination with the release of material, non-public information.

The exercise price of our options to purchase shares of our common stock must be equal to the fair market value (our closing price on the Nasdaq Global Select Market) of our common stock on the date of grant.

Performance-Based Incentive Awards

From time to time as it determines appropriate, the Compensation Committee may grant additional long-term cash or equity incentive opportunities intended to drive attainment of key performance goals over a multi-year period. In 2017, the Compensation Committee approved a long-term incentive program designed to

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incentivize achievement of regulatory approvals for enfortumab vedotin and tisotumab vedotin, two key company milestones. The target values for the plan are based on the approximate full year bonus target applicable for each individual executive’s grade level. The Compensation Committee selected this approach to setting target value because the Compensation Committee previously used the same approach with respect to long-term incentive plans it previously approved in 2010 and 2016, and continues to see this approach as an effective means to reach its incentive and retention goals for this plan. This program is described further below under “—2017 Compensation Decisions for the Named Executive Officers—Performance-Based Incentive Awards.”

Until February 2018, we also maintained a third special long-term incentive program that offered cash and equity awards that would have become payable, or subject to grant, as applicable if we achieved designated performance goals relating to SGN-CD33A. No payments were made under this program, and it was terminated in February 2018, as a result of our decision to discontinue the phase 3 CASCADE clinical trial of SGN-CD33A in frontline older acute myeloid leukemia patients.

2017 Compensation Decisions for the Named Executive Officers

We believe that 2017 was a productive year for us due in part to the successful ECHELON-1 topline data release, progress on key corporate phase 3 trials of ADCETRIS and pivotal trials of enfortumab vedotin and tisotumab vedotin, and the additional progress we made advancing our clinical development pipeline projects, as described above under the heading “—Executive Summary.”

Base Salary

The following table sets forth the base salaries effective for each of our Named Executive Officers that were approved by the Compensation Committee in January 2017 and became effective as of and the percentages that their base salaries were increased from their 2016 base salary levels.

In January 2017, the Compensation Committee approved a merit increase of 4% to our CEO’s base salary in recognition of his role in leading the achievement of our strong corporate performance and following its analysis of competitive market data based on the peer group salary levels. In determining base salary for Dr. Siegall and each of the executive officers below, the Compensation Committee first referenced the 50^th percentile and then adjusted for other factors including the aspects of individual performance further described below.

With respect to Mr. Simpson, the Compensation Committee focused on his leadership in our finance, investor relations, and facilities/real estate functions. In January 2017, the Compensation Committee approved a merit increase of 3.5% to Mr. Simpson’s base salary.

With respect to Dr. Drachman, the Compensation Committee focused on his leadership in research and development. In January 2017, the Compensation Committee approved a merit increase of 3.76% to Dr. Drachman’s base salary.

With respect to Dr. Himes, the Compensation Committee focused on his leadership in technical operations and manufacturing. In January 2017, the Compensation Committee approved a merit increase of 4% to Dr. Himes’ base salary.

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With respect to Ms. Liu, the Compensation Committee focused on her leadership in legal affairs and transactional matters. In January 2017, the Compensation Committee approved a merit increase of 4.64% to Ms. Liu’s base salary.

With respect to Mr. Dobmeier, the Compensation Committee focused on his oversight of the Company’s operations, corporate communications and investor relations initiatives and his contribution to our business development activities. In January 2017, the Compensation Committee approved a merit increase of 3.75% to Mr. Dobmeier’s base salary. Mr. Dobmeier transitioned from an 85% of full-time schedule to a full-time schedule on September 1, 2017.

Annual Cash Incentive Awards

The target annual cash incentive award opportunities for our Named Executive Officers for 2017 are set forth in the table below. These targets were set based on market data from our 2016 peer group for similar positions. There were no changes from 2016 targets (as a percentage of base salary) because the Compensation Committee determined that such target percentages continued to be appropriate.

The corporate performance goals established under the Executive Bonus Plan in 2017 were primarily based on sales of ADCETRIS, the advancement of development and clinical activities related to ADCETRIS, SGN-CD33A, enfortumab vedotin and our additional product candidates, business development and expansion of operations, expense management and stock performance, all of which the Compensation Committee believes strongly relate to the creation of stockholder value. Our performance goals in 2017 were as set forth below. The ADCETRIS goal was weighted at 40%, the SGN-CD33A goal was weighted at 20%, the enfortumab vedotin goal was weighted at 12.5%, the pipeline goal was weighted at 10% and business and operations goals were weighted at 17.5%. An additional goal with respect to tisotumab vedotin was also considered.

The ADCETRIS goal included the following targets:

The SGN-CD33A goal included the following targets:

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The enfortumab vedotin goal included the following targets:

The product pipeline included the following targets:

The business and operations goals included the following targets:

In August 2017, in light of the company’s anticipated decision to exercise our option to co-develop tisotumab vedotin with Genmab, the Board added a goal with respect to this program. This goal did not replace any other goals, but rather was an additional goal, and was not given a specific weighting for purposes of the Executive Bonus Plan:

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The Compensation Committee determined that we met the majority of our performance goals for 2017. Specifically, the Compensation Committee determined that we met or exceeded all of the goals with respect to ADCETRIS, enfortumab vedotin and tisotumab vedotin. The Compensation Committee determined that we also met all of our goals relating to our pipeline, except with respect to SGN-CD123A and SGN-CD352, which did not meet the timing set forth in the goals, and that we met or exceeded all goals relating to our business and operations with the exception of our business development goals that were partially achieved, and our stock performance goal, which was not achieved. However, the Compensation Committee determined that none of our goals with respect to SGN-CD33A were achieved as a result of the Company’s decision to discontinue the phase 3 CASCADE clinical trial of SGN-CD33A in frontline older acute myeloid leukemia patients and suspend the development of SGN-CD33A pending further evaluation. The Compensation Committee considered the fact that this goal was not achieved in determining the total amount of goal achievement. The 2017 performance goals were aggressive and set at challenging levels such that the attainment of executive target annual cash incentive award opportunities was not assured at the time they were set and would require a high level of effort and execution on the part of the executive officers in order to achieve the goals. In light of the strong performance with respect to our goals other than those relating to SGN-CD33A, the achievement of the tisotumab vedotin goals despite having less than a full year to do so, and the challenging nature of the goals, the Compensation Committee determined our corporate performance percentage to be 105% for 2017.

For 2017, based on the Compensation Committee’s evaluation of individual performance as well as individual executive contributions to our corporate goal achievement and our strong performance in 2017, the individual performance factors for our Named Executive Officers were determined to be 115% for Dr. Himes, 110% for Mr. Simpson and Ms. Liu and 95% for Dr. Drachman. The Compensation Committee did not establish an individual performance factor for Mr. Dobmeier, as his last day of employment was December 14, 2017 and he was therefore ineligible to receive an award under the Executive Bonus Plan. Dr. Siegall’s overall annual cash incentive award percentage was 105%, equaling a 2017 annual cash incentive award of $934,500, Mr. Simpson’s overall annual cash incentive award percentage was 107%, equaling a 2017 annual cash incentive award of $264,076, Dr. Drachman’s overall target annual cash incentive award percentage was 101%, equaling a 2017 annual cash incentive award of $268,382, Dr. Himes’ overall target annual cash incentive award percentage was 109%, equaling a 2017 annual cash incentive award of $260,728, and Ms. Liu’s overall target annual cash incentive award percentage was 107%, equaling a 2017 annual cash incentive award of $223,175.

Long-Term Equity Awards

In line with our typical practice, the equity awards granted to our executive officers in 2017 included a 50/50 combination of options to purchase shares of our common stock and RSU awards that may be settled for shares of our common stock.

In August 2017, the Compensation Committee considered the grant of annual equity awards to our executive officers after reviewing a competitive market analysis prepared by Compensia and referencing the 50^th percentile for each role, the recommendations of our CEO based on his evaluation of their individual performance, the executive officer’s prior grant levels and the extent to which the executive officer is currently vested in his or her stock awards, scope and criticality of role and parity among executives in roles of a given level.

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The table below shows the number of shares subject to the stock options and RSU awards granted to our Named Executive Officers in August 2017 (other than pursuant to the special EV/TV LTIP described separately below), as well as the total grant date fair value of these awards on the applicable date of grant.

The options to purchase shares of our common stock granted to our Named Executive Officers in 2017 vest as to 25% of the shares subject to the option upon the first anniversary of the grant date and as to 1/36th of the remaining shares subject to the option each month thereafter until such grant is fully vested on the fourth anniversary of the grant date. Such options are also subject to vesting acceleration as described under “—Post-Employment Compensation” below.

The exercise price of the options granted to our executive officers in 2017 equaled the fair market value of our common stock, our closing price on the Nasdaq Global Select Market, on the date of grant.

RSU awards granted to our Named Executive Officers in 2017 vest in full on the third anniversary of the grant date, subject to vesting acceleration as described under “—Post-Employment Compensation” below.

Performance-Based Incentive Awards

On September 29, 2017, the Compensation Committee approved the EV/TV LTIP for the purpose of incentivizing the Company’s employees to achieve regulatory approvals of (i) enfortumab vedotin, a product candidate currently being co-developed by the Company and Astellas under the Company’s collaboration and license agreement with Astellas (the “EV Collaboration Agreement”), and (ii) tisotumab vedotin, a product candidate currently being co-developed by the Company and Genmab under the Company’s collaboration and license agreement with Genmab (the “TV Collaboration Agreement”).

Under the EV/TV LTIP, each Named Executive Officer is eligible to receive a cash award and an RSU award that may be settled for shares of our common stock.

The Compensation Committee designed the EV/TV LTIP to include an award to executive officers that is 50% cash and 50% RSUs based on the long term nature of the goal and the additional retentive value that can be provided by RSU awards.

A portion of each cash award will become payable, and a portion of each RSU award will be granted, only upon certification by the Compensation Committee that the FDA has approved enfortumab vedotin (such approval, the “EV Approval Milestone”), and the remaining portion of each cash award will become payable, and the remaining portion of each RSU award will be granted, only upon certification by the Compensation

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Committee that the FDA has approved tisotumab vedotin (such achievement, the “TV Approval Milestone” and together with the EV Approval Milestone, the “Milestones”), provided in each case that the Named Executive Officer is still actively employed by the Company. The Compensation Committee selected these milestones because of their importance to our long-term business strategy and have the potential, if achieved, to drive increases in stockholder value. Any RSU awards granted due to achievement of a Milestone will vest on the second anniversary of the occurrence of such Milestone, provided that the Named Executive Officer’s continuous service with the Company or any of its subsidiaries has not terminated prior to the vesting date. The vesting of any granted RSU awards is subject to full acceleration in the event of a termination of service (without cause or due to constructive termination) immediately prior to, or within twelve months after, a change of control of the Company, or in the event an acquirer in a change of control of the Company fails to assume the RSU awards. If a Milestone is not achieved by a specified date, then no cash or RSU awards will be paid or granted with respect to such Milestone. In addition, in the event that the Company exercises its right to terminate its co-funding obligations with respect to enfortumab vedotin under the EV Collaboration Agreement (an “EV Opt-Out”) prior to the achievement of the EV Approval Milestone, or with respect to tisotumab vedotin under the TV Collaboration Agreement (a “TV Opt-Out”) prior to the achievement of the TV Approval Milestone, then no cash or RSU awards will be paid or granted with respect to such Milestone. If both an EV Opt-Out and a TV Opt-Out occur, then the EV/TV LTIP will automatically terminate on the later to occur of the date of the EV Opt-Out and the date of the TV Opt-Out. Likewise, the EV/TV LTIP will automatically terminate if neither Milestone is achieved by a specified date. Any RSU awards provided pursuant to the EV/TV LTIP will be granted under, and subject to the terms of, the Restated 2007 Plan.

The total target award value (expressed in dollars) for an employee with respect to the cash award and restricted stock unit award, if any (the “Target Award Value”), is set pursuant to the terms of the EV/TV LTIP based on the employee’s position level with the Company or its subsidiaries as of the earlier of the date that the EV BLA is submitted to the FDA and the date that the TV BLA is submitted to the FDA. The target values for the plan are based on the approximate full year bonus target applicable for each individual executive’s grade level. The Compensation Committee selected this approach to setting target value because the bonus target values were developed based on peer group data, and because we previously used this same approach with respect to previously established long-term incentive plans in 2010 and 2016. Actual award values, on a sliding scale from 0% to 120% of the Target Award Value, are calculated based on the dates of achievement of each Milestone.

The amount of cash paid, if any, with respect to the EV Approval Milestone for the Named Executive Officers will be equal to 50% of the participant’s Target Award Value, multiplied by a specified percentage with respect to such Milestone, multiplied by the applicable earn out percentage from the sliding scale. The amount of cash paid, if any, with respect to the TV Approval Milestone for executive officers will be equal to 50% of the participant’s Target Award Value, multiplied by a specified percentage with respect to such Milestone, multiplied by the applicable earn out percentage from the sliding scale. The number of restricted stock units granted, if any, with respect to the EV Approval Milestone for executive officers will be equal to 50% of the participant’s Target Award Value, multiplied by a specified percentage with respect to such Milestone, multiplied by the applicable earn out percentage from the sliding scale, with the product of these numbers then divided by the closing price of the Company’s common stock on the date of grant. The number of restricted stock units granted, if any, with respect to the TV Approval Milestone for executive officers will be equal to 50% of the participant’s Target Award Value, multiplied by a specified percentage with respect to such Milestone, multiplied by the applicable earn out percentage from the sliding scale, with the product of these numbers then divided by the closing price of the Company’s common stock on the date of grant. The specified percentages with respect to the Milestones together equal 100%. The Target Award Values for our Named Executive Officers were set based on consideration of the value of these programs to the Company and the overall cash incentive targets for our executive officers.

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The Target Award Values for our Named Executive Officers are as follows:

Health and Welfare Benefits

All of our Named Executive Officers are eligible to receive our standard employee benefits, such as our Section 401(k) plan, medical, dental, vision coverage, short-term disability, long-term disability, group life insurance, cafeteria plan, and the ESPP, in each case on the same basis as our other employees, including the matching contributions provided under our Section 401(k) plan. We make a matching contribution equal to 75% of each employee’s salary deferral contribution up to 6% of the employee’s compensation, subject to the applicable statutory limit. The matched contribution is subject to a vesting period of four years, with vesting occurring at a rate of 25% per year. Following four years of employment with the Company, all existing and future matching contributions to the Section 401(k) plan are fully vested.

Employment Agreements

We are a party to employment agreements with each of our Named Executive Officers. As further described below, when establishing the termination and change of control provisions in our agreements with our Named Executive Officers, the Compensation Committee considered industry practice.

Post-Employment Compensation

We provide severance benefit protection to our Named Executive Officers through our individual employment agreements with each such individual.

The Compensation Committee believes these severance payments and benefits are important from a retention perspective to provide some level of protection to our executive officers from having their employment terminated without cause or constructively terminated prior to or after a change in control of the Company, or from experiencing a life-changing disability, and that the amounts are reasonable when compared with similar arrangements adopted by other biotechnology companies. In addition, the Compensation Committee believes that these severance payments and benefits align our executive officer and stockholder interests by enabling them to consider corporate objectives and possible transactions that are in the best interests of the stockholders and other constituents of the Company without undue concern over whether such objectives or transactions may jeopardize their own employment.

With these arrangements, the Compensation Committee sought uniformity of terms among our executive officers based on their positions at the Company, with only our CEO receiving vesting acceleration benefits solely as a result of a change in control of the Company. In addition, the Compensation Committee believes that the payment-triggering event outside of the death or disability context, namely, being terminated without cause or constructively terminated, and then only when there is no misconduct by the executive officer, is a fair hurdle for the ensuing rewards. Further, our CEO’s full acceleration of vesting of stock awards upon a change in control

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of the Company is intended to reduce the concern that he may not have a comparable position in an acquiring company as a result of the change of control.

More information regarding these arrangements is provided under the heading “—Potential Payments Upon Termination or Change-in-Control—Employment Agreements.”

Tax and Accounting Considerations

Deduction Limitation

Prior to December 22, 2017, when the Tax Cuts and Jobs Act of 2017 (“TCJA”) was signed into law, Section 162(m) of the Internal Revenue Code of 1986, as amended (the “IRC”), limited the corporate deduction of publicly traded entities for federal income tax purposes to not more than $1 million of compensation paid to certain executive officers in a calendar year. Compensation above $1 million could be deducted if it was “performance-based compensation.” Under the TCJA, the performance-based exception has been repealed and the $1 million deduction limit now applies to anyone serving as the chief executive officer or the chief financial officer at any time during the taxable year, and the top three other highest compensated executive officers serving at fiscal year-end. The new rules generally apply to taxable years beginning after December 31, 2017. The TCJA also provides for transitional guidance that will allow certain payments made under written and binding agreements entered into prior to November 2, 2017 to be treated as if they were made under the provisions of Section 162(m) that were in effect prior to enactment of the TJCA.

Prior to the TCJA, the Compensation Committee had not adopted a policy requiring all executive compensation to be deductible, in order to maintain flexibility in compensating our executive officers in a manner designed to promote our objectives. Going forward, while the Compensation Committee intends to evaluate the effects of the revised compensation limits of Section 162(m) on any compensation it proposes to grant, the Compensation Committee intends to continue to provide future compensation in a manner consistent with our best interests and those of our shareholders, including compensation that is potentially not deductible.

Accounting Considerations

We follow Financial Accounting Standards Board ASC Topic 718 for our stock-based compensation awards. In accordance with ASC Topic 718, stock-based compensation cost is measured at the grant date, or with respect to performance-based awards, the service inception date, based on the estimated fair value of the awards using a variety of assumptions. This calculation is performed for accounting purposes and, as applicable, reported in the compensation tables, even though recipients may never realize any value from their awards. We expect to record this expense on an ongoing basis over the requisite employee service period. For performance-based stock options, we expect to record compensation expense over the estimated service period once the achievement of the performance based milestone is considered probable. At each reporting date, we assess whether achievement of a milestone is considered probable, and if so, record compensation expense based on the portion of the service period elapsed to date with respect to that milestone, with a cumulative catch-up, net of estimated forfeitures. We will recognize remaining compensation expense with respect to a milestone, if any, over the remaining estimated service period. Accounting rules also require us to record cash compensation as an expense at the time the obligation is incurred.

Stock Ownership Guidelines

Our CEO is required to own, directly or indirectly, a number of shares of our common stock with a value of not less than five times his base salary as of December 31 of each year. As of December 31, 2017, our CEO was in compliance with this stock ownership requirement. In 2017, on the recommendation of the Nominating and Corporate Governance Committee, the Board adopted stock ownership guidelines requiring our executive officers other than our CEO to own, directly or indirectly, a number of shares of our common stock with a value

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of not less than one and a half times such executive’s annual base salary. Our executives are required to be in compliance with the stock ownership requirement by December 31st of the fifth year following the year during which such individual becomes subject to these ownership guidelines. Our currently serving executive officers first became subject to these guidelines during 2017, and will be required to be in compliance by December 31, 2022. Any future executive officer will first become subject to these guidelines on the date such officer commences employment with us.

Prohibitions on Hedging and Pledging

Pursuant to our insider trading policy, we prohibit our executive officers and the members of our Board of Directors from engaging in short-term speculative transactions and further prohibit them from hedging or pledging our securities as collateral.

Compensation Recovery Policy

Currently, we do not have a policy to recover incentive compensation paid to our executive officers in the event of a financial restatement. We will comply with the requirements of the Dodd-Frank Act and will adopt a compensation recovery policy in accordance with such requirements once the SEC adopts final regulations on the subject.

As a public company subject to the provisions of Section 304 of the Sarbanes-Oxley Act of 2002, if we are required as a result of misconduct to restate our financial results due to our material noncompliance with any financial reporting requirements under the federal securities laws, our Chief Executive Officer and Chief Financial Officer may be legally required to reimburse us for any bonus or other incentive-based or equity-based compensation they receive.

Compensation and Risk

We believe that the risks arising from our compensation policies and practices are not reasonably likely to have a material adverse effect on the Company. In addition, the Compensation Committee believes that the mix and design of the elements of executive compensation do not encourage our employees to assume excessive risks.

The Compensation Committee periodically reviews the elements of executive compensation to determine whether any portion of executive compensation encourage excessive risk taking. The Compensation Committee most recently conducted this review in January 2018 and concluded that it does not. Among the factors that the Compensation Committee considered were:

Summary

The Compensation Committee believes that our compensation philosophy and programs are designed to foster a performance-oriented culture that aligns employees’ interests with those of our stockholders. The Compensation Committee believes that the compensation of our executives is both appropriate and responsive to the goal of improving stockholder value.

COMPENSATION COMMITTEE REPORT (1)

The Compensation Committee has reviewed and discussed the foregoing Compensation Discussion and Analysis required by Item 402(b) of Regulation S-K with management and, based on such review and

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discussions, the Compensation Committee has recommended to our Board of Directors that the Compensation Discussion and Analysis be included in this Proxy Statement and incorporated into our Annual Report on Form 10-K for the fiscal year ended December 31, 2017.

Submitted by the members of the Compensation Committee:

Felix Baker, Ph.D. (chairman)

John A. Orwin

Daniel G. Welch

COMPENSATION COMMITTEE INTERLOCKS AND INSIDER PARTICIPATION

During 2017, the Compensation Committee consisted of Felix Baker (chairman), John A. Orwin and Daniel G. Welch, none of whom is a current or former officer or employee of Seattle Genetics. Please refer to the section of this proxy statement entitled “Certain Relationships and Related Party Transactions” for information concerning certain transactions involving entities affiliated with Dr. Baker.

During 2017, no member of the Compensation Committee or executive officer of Seattle Genetics has or had a relationship that would constitute an interlocking relationship with executive officers or directors of another entity.

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SUMMARY COMPENSATION TABLE

The following table sets forth all of the compensation awarded to, or earned by, our “Named Executive Officers.”

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GRANTS OF PLAN-BASED AWARDS

The following table sets forth each equity and non-equity award granted to our Named Executive Officers during 2017.

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EMPLOYMENT AGREEMENTS AND ARRANGEMENTS

Employment Agreements. Each of our Named Executive Officers has entered into a written employment agreement with Seattle Genetics. For a description of these employment agreements, please see the section of this proxy statement under the heading “Potential Payments Upon Termination or Change-In-Control—Employment Agreements” below.

Annual Cash Bonus Awards. We have adopted our Executive Annual Bonus Plan that provides for annual bonus awards to reward executive officers based on our achievement of specific corporate goals and their achievement of individual performance goals. For more information regarding our Executive Annual Bonus Plan, please see the section of this proxy statement under the heading “—Compensation Discussion and Analysis—Principal Elements of Compensation—Annual Cash Incentive Awards” and footnote (2) to the Grants of Plan-Based Awards table above.

Stock Awards. Discretionary options that we granted in 2017 under the 2007 Plan have a ten year term and vest as to 1/4^th of the shares subject to the options on the one year anniversary of the grant date and 1/36^th of the remaining shares each month thereafter until such option is fully vested on the four year anniversary of the grant date, subject to the accelerated vesting of such options under the terms of each executive’s employment

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agreement with us and pursuant to the 2007 Plan. Performance-based stock options that we granted in 2017 vest in accordance with the terms set forth in the ECHELON-1 LTIP (as defined below) and were also granted under the 2007 Plan. Options granted under the 2007 Plan carry an exercise price equal to the fair market value on the date of grant (generally the closing price of our common stock on the grant date on the Nasdaq Global Select Market), and the 2007 Plan permits the exercise price of stock options to be paid by cash, check, wire transfer, other shares of our common stock (with some restrictions), broker assisted same-day sales, cancellation of debt, cashless “net exercise” arrangements, and any other form of consideration permitted by applicable law. If an executive’s service with us terminates for any reason other than cause, death or disability, then options held by the executive under the 2007 Plan generally will be exercisable to the extent they are vested on the termination date for a period of three months after the termination (if an executive’s service with us terminates for cause, then the Board or the Compensation Committee has the authority to terminate all options held by the executive under the 2007 Plan immediately). Generally, if an executive’s service with us terminates as a result of the executive’s death or in the event of the executive’s death within 30 days following the executive’s termination of service, all outstanding options that were vested and exercisable as of the date of the executive’s death or termination of service, if earlier, may be exercised for six months following the executive’s death but in no event after the expiration date of such option. Generally, if an executive’s service with us terminates as a result of the executive’s disability, then all options to the extent they are vested and exercisable on the termination date may be exercised for one year following the termination date but in no event after the expiration date of such option. Each RSU represents a right to receive one share of our common stock (subject to adjustment for certain specified changes in our capital structure). In the event that RSUs vest, we will deliver one share of our common stock for each RSU that has vested. Discretionary RSUs that we granted in 2017 generally vest in full on the third anniversary of the grant date, provided that vesting will cease if an executive’s service with us terminates for any reason.

Under the 2007 Plan, in the event of (i) an acquisition of Seattle Genetics by means of any reorganization, merger or consolidation but excluding any merger effected exclusively for the purpose of changing the domicile of the company, (ii) any sale of all or substantially all of our assets or (iii) any other event specified by the plan administrator, so long as in either (i) or (ii), our stockholders of record immediately prior to the transaction hold less than 50% of the voting power of the surviving entity and, so long as in (iii) that no change in control shall be deemed to occur upon announcement or commencement of a tender offer or upon a “potential” takeover or upon stockholder approval of a merger or other transaction, in each case without a requirement that the change in control actually occur, then the Board or the compensation committee may, in its discretion: (i) provide for the assumption or substitution of, or adjustment (including to the number and type of shares and exercise price applicable) to, each outstanding equity award; (ii) accelerate the vesting of equity awards; and/or (iii) provide for termination of awards as a result of the change in control on such terms and conditions as it deems appropriate, including providing for the cancellation of awards for a cash or other payment to the executive.

Additionally, (i) if the successor corporation does not assume or substitute equivalent awards for all outstanding equity awards granted pursuant to the 2007 Plan, then as of the date of completion of the acquisition or merger, the vesting of such equity awards will be accelerated in full; and (ii) if outstanding equity awards are assumed or equivalent awards are substituted by the successor corporation and if at the time of, immediately prior to or within twelve months after the effective time of the change of control, an equity awardee’s service as an employee or consultant is terminated without cause or due to constructive termination, then the vesting of such substituted equity award will be accelerated in full.

For more information regarding grants of equity awards to our Named Executive Officers, please see the section of this proxy statement under the headings “—Compensation Discussion and Analysis—Principal Elements of Compensation—Long-Term Equity Awards” and “—Compensation Discussion and Analysis—Post-Employment Compensation” above.

Long-Term Incentive Plans. In May 2016, the Compensation Committee approved the ECHELON-1 LTIP. Under the ECHELON-1 LTIP, each employee, including each Named Executive Officer, is eligible to

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receive a cash award and an option to purchase shares of our common stock, with the amount of each cash and option award based on the participant’s position with the Company. The cash awards will be payable to participants in the ECHELON-1 LTIP if the Approval Milestone is achieved by December 31, 2019 and will be paid following the Compensation Committee’s certification of the achievement of the Approval Milestone, provided that the participant is still actively employed by the Company and is in good standing as of the payment date. If the Approval Milestone is not achieved by December 31, 2019, the cash awards will be forfeited. The ECHELON-1 LTIP options, which were granted to our Named Executive Officer participants in ECHELON-1 LTIP on May 9, 2016 with an exercise price of $34.20 per share (the fair market value of our common stock on the date of grant), will commence vesting, if at all, upon the Compensation Committee’s certification of the achievement of the Approval Milestone, and will vest in four equal annual installments on the first four anniversaries of the date the Approval Milestone is achieved, subject to continuous service with the Company as of each vesting date. If the Approval Milestone is not achieved by December 31, 2019, the options will be forfeited.

In September 2017, the Compensation Committee approved the EV/TV LTIP. Under the EV/TV LTIP, each employee, including each Named Executive Officer, is eligible to receive a cash award and, and depending on the participant’s position with the company, may also be eligible for an RSU award. A portion of each cash award will become payable, and a portion of each RSU award will be granted, only upon certification by the Compensation Committee that the FDA has approved enfortumab vedotin, and the remaining portion of each cash award will become payable, and the remaining portion of each RSU award will be granted, only upon certification by the Compensation Committee that the FDA has approved tisotumab vedotin, provided that the participant is still actively employed by the Company and is in good standing as of each applicable payment date. Any RSU award granted due to achievement of a milestone will vest on the second anniversary of the occurrence of such milestone, subject to continuous service with the Company through the vesting date. If a particular milestone is not achieved by a specified date with respect to such milestone, then no cash award will be made nor will an RSU award be granted with respect to such milestone.

For more information regarding the EV/TV LTIP, please see the section of this proxy statement under the “Compensation Discussion and Analysis—Principal Elements of Compensation—Long-Term Equity Awards” and footnotes (4) and (5) to the Grants of Plan-Based Awards table above.

Other Compensatory Arrangements. Seattle Genetics pays the life insurance premium for all of its employees, including the executive officers. In addition, Seattle Genetics matches 75% of the first 6% of salary contributed to Seattle Genetics’ 401(k) plan by employees, including the executive officers. The matched contributions vest at 25% annually, such that employees are fully vested after four years from their date of hire. From time to time, individual executives negotiate other compensatory arrangements in connection with their initial hire.

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OUTSTANDING EQUITY AWARDS AT FISCAL YEAR-END

The following table sets forth certain information regarding equity awards granted to the Named Executive Officers that were outstanding as of December 31, 2017.