OS Therapies (NYSE-A: OSTX) (“OS Therapies” or “the Company”), a clinical-stage immunotherapy and Antibody Drug Conjugate (ADC) biopharmaceutical company, today announced the launch of OS Animal Health, Inc., a wholly owned subsidiary focused on commercializing OST-HER2 for the treatment of canine osteosarcoma.

• OST-HER2 market opportunity in canine osteosarcoma exceeds $150 million
• Recent data in prevention of amputation in frontline canine osteosarcoma and control of metastatic osteosarcoma adds to historical data that supported prior conditional approval related to increase in overall survival (OS) post-amputation
• Updated commercial manufacturing process to be used in pending new USDA conditional approval application for frontline, metastatic and OS in osteosarcoma

OST-HER2 is an off-the-shelf immunotherapy candidate that has shown positive clinical data in both human pediatric and canine osteosarcoma. Parent company OS Therapies is advancing towards an FDA Accelerated Approval submission, anticipated in the third quarter of 2025, for the prevention of recurrence in pediatric patients with fully resected, lung-metastatic osteosarcoma. Concurrently, its wholly-owned subsidiary, OS Animal Health, is focused on re-establishing USDA conditional approval for OST-HER2 in canine osteosarcoma, with a targeted submission in the second half of 2025.

“Osteosarcoma is the most common canine cancer, affecting more than 40,000 dogs in the U.S. each year,” said Paul Romness, CEO of OS Therapies. “Given the recent issuance of a new patent protecting the commercial manufacturing process for OST-HER2 and the rest of our listeria immunotherapy platform into 2040, we now have a clear commercial opportunity to greatly improve health outcomes in this deadly canine cancer through OS Animal Health.”

To advance OST-HER2 in the veterinary space with the attention it deserves, OS Animal Health will operate independently from the parent company, with separate funding aligned to the needs of the animal health market.

“Selling into the animal health cancer market is substantially different than selling into the human cancer market, and as such we have created this new corporate structure that will be capitalized separately and independently from the parent company’s balance sheet so that we can deliver on this unique market opportunity without diluting OS Therapies share structure,” Mr. Romness added. “Our current animal health advisors are providing the clinical and regulatory expertise we need to move the USDA process forward. We expect OS Animal Health to begin generating revenue as early as 2025.”

According to Grandview Research, the veterinary oncology market is valued at 1.57 billion, with canine osteosarcoma representing 86% of the total – approximately $1.35 billion. OS Therapies estimates OST-HER2’s addressable opportunity in U.S. canine osteosarcoma to be over $150 million.

The canine osteosarcoma treatment market is currently dominated by chemotherapy, radiation therapy, and surgical procedures such as amputation and tumor resection – approaches that often result in limited overall survival outcomes. OST-HER2 has the potential to significantly improve how this aggressive cancer is treated in dogs, offering a less invasive and more targeted alternative to current options.

OST-HER2 is also featured in the PBS documentary Shelter Me: The Cancer Pioneers, which offers a look into canine comparative oncology, a field that compares treatment of cancers in dogs to those in people and covers developing treatments for rare forms of cancer. The movie is available via streaming on the PBS website.

OST-HER2, being developed by parent company OS Therapies, Inc. for pediatric osteosarcoma, has received Rare Pediatric Disease Designation (RPDD) for osteosarcoma from the US FDA, and if it receives a conditional BLA via Accelerated Review prior to September 30, 2026, it will become eligible to receive a Priority Review Voucher (PRV) that it intends to immediately sell. The most recent PRV sale, valued at $155 million, occurred in May 2025.

About OS Therapies

OS Therapies is a clinical stage oncology company focused on the identification, development, and commercialization of treatments for osteosarcoma 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 US Food & Drug Administration and Fast-Track and Orphan Drug designations from the US FDA and European Medicines Agency. The Company has demonstrated 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 BLA to the US 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 silicone Si-Linker and Conditionally Active Payload (CAP) technology, enabling the delivery of multiple payloads per linker. 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 news 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 US FDA and grant of a priority review voucher and other risks and uncertainties described in “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” in the Company’s registration statement on Form S-1 filed with the Securities and Exchange Commission (the “SEC”) on November 12, 2024, as amended on November 27, 2024, and other subsequent documents we file with the SEC, including but not limited to our Quarterly Reports on Form 10-Q. 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.

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