• Final FDA Type C Meeting December 11, 2025 - biomarker data to be available
• October 10, 2025 FDA/Osteosarcoma Institute Workshop narrows focus for OST-HER2 overall survival, biomarker correlation & canine osteosarcoma data

New York, New York--(Newsfile Corp. - October 17, 2025) - OS Therapies Inc. (NYSE American: OSTX) ("OS Therapies" or "the Company"), a clinical-stage cancer immunotherapy and antibody drug conjugate biotechnology company, today announced that the United States Food & Drug Administration ("FDA") has granted a second Type C Meeting, following its successful End of Phase 2 Meeting. The primary purpose of the meeting is to gain alignment on the clinical efficacy data endpoints to support a Biologics Licensing Application ("BLA") under the Accelerated Approval Program ("Accelerated Approval") for OST-HER2 following a successful Phase 2b clinical trial in the prevention or delay of recurrent, fully resected, pulmonary metastatic osteosarcoma (the "Metastatic Osteosarcoma Program"). The meeting is scheduled for December 11, 2025, which allows for sufficient time for the Company to receive biomarker data from the Phase 2b trial to correlate immune activation with clinical outcomes.

Concurrently, the United Kingdom's Medicines and Healthcare products Regulatory Agency ("MHRA") granted a pre-Marketing Authorization Application ("pre-MAA") Meeting for OST-HER2 Metastatic Osteosarcoma Program. The Company will be reviewing the data it has submitted as part of an expected rolling review process targeted to begin in November 2025. This Company is seeking to align BLA and MAA submission timing, in accordance with Project Orbis.

"We believe the recent FDA / Osteosarcoma Institute Workshop was a great forum that moved the field to focus on areas where meaningful clinical progress can be made in the near-term, given the shortage of treatment options available," said Paul Romness, MPH, Chairman & CEO of OS Therapies. "We were pleased to see consensus gained on the value of the canine osteosarcoma model, given its similarity to human osteosarcoma that has jumpstarted the Comparative Oncology Field. Consensus was gained on the need to focus on overall survival data as the ultimate efficacy outcome endpoint. Significant time was also spent discussing clinical trial designs that could be more appropriate for the immunotherapies and targeted cytotoxic drugs of the future, as compared with the chemotherapies of the past. We believe FDA's August 18, 2025 Overall Survival in Oncology Clinical Trials guidance is exactly what the field needed to focus on what matters most to patients: long term survival and quality of life."

About OS Therapies

OS Therapies is a clinical stage oncology company focused on the identification, development, and commercialization of treatments for Osteosarcoma (OS) and other solid tumors. OST-HER2, the Company's lead asset, is an immunotherapy leveraging the immune-stimulatory effects of Listeria bacteria to initiate a strong immune response targeting the HER2 protein. OST-HER2 has received Rare Pediatric Disease Designation (RPDD) from the U.S. Food & Drug Administration and Fast-Track and Orphan Drug designations from the U.S. FDA and European Medicines Agency. The Company reported positive data in its Phase 2b clinical trial of OST-HER2 in recurrent, fully resected, lung metastatic osteosarcoma, demonstrating statistically significant benefit in the 12-month event free survival (EFS) primary endpoint of the study. The Company anticipates submitting a Biologics Licensing Application (BLA) to the U.S. FDA for OST-HER2 in osteosarcoma in 2025 and, if approved, would become eligible to receive a Priority Review Voucher that it could then sell. OST-HER2 has completed a Phase 1 clinical study primarily in breast cancer patients, in addition to showing preclinical efficacy data in various models of breast cancer. OST-HER2 has been conditionally approved by the U.S. Department of Agriculture for the treatment of canines with osteosarcoma.

In addition, OS Therapies is advancing its next-generation Antibody Drug Conjugate (ADC) and Drug Conjugates (DC), known as tunable ADC (tADC), which features tunable, tailored antibody-linker-payload candidates. This platform leverages the Company's proprietary ph-sensitive silicone Si-Linker and Conditionally Active Payload (CAP) technology, enabling the delivery of multiple tri-specific payloads. For more information, please visit www.ostherapies.com.

Forward-Looking Statements

Statements in this press release about future expectations, plans and prospects, as well as any other statements regarding matters that are not historical facts, may constitute forward-looking statements within the meaning of the federal securities laws. These forward-looking statements and terms such as "anticipate," "expect," "intend," "may," "will," "should" or other comparable terms involve risks and uncertainties because they relate to events and depend on circumstances that will occur in the future. Those statements include statements regarding the intent, belief or current expectations of OS Therapies and members of its management, as well as the assumptions on which such statements are based. OS Therapies cautions readers that forward-looking statements are based on management's expectations and assumptions as of the date of this press release and are subject to certain risks and uncertainties that could cause actual results to differ materially, including, but not limited to the approval of OST-HER2 by the U.S. FDA and other risks and uncertainties described in "Risk Factors" in the Company's most recent Annual Report on Form 10-K, most recent Quarterly Report on Form 10-Q and other subsequent documents the Company files with the Securities and Exchange Commission. Any forward-looking statements contained in this press release speak only as of the date hereof, and, except as required by the federal securities laws, OS Therapies specifically disclaims any obligation to update any forward-looking statement, whether as a result of new information, future events or otherwise.

To view the source version of this press release, please visit https://www.newsfilecorp.com/release/270842