• Company finalizing preparations for end of January 2026 U.S. FDA Biologics License Application (BLA) submission for OST-HER2 program in the prevention or delay of recurrent, fully resected, pulmonary metastatic osteosarcoma (Metastatic Osteosarcoma Program) under Accelerated Approval Program
• Biomarker data from Phase 2b Metastatic Osteosarcoma Program human clinical trial expected to be released during week of J.P. Morgan Healthcare Conference 2026
• UK and EU Marketing Authorisation Application (MAA) submissions for conditional approval expected by end of February 2026 and March 2026, respectively
• Company expects to participate in multiple H1 2026 meetings with U.S. FDA, U.K. MHRA and Europe's EMA as part of processes to gain regulatory approvals
• OS Animal Health 'go-public' transaction SEC filing expected in early January 2026
• Delayed data from OST-504 Phase 1 trial in castration resistant prostate cancer expected in Q1 2026 after prioritizing biomarker lab partner resources for osteosarcoma data analysis, with End of Phase 1 FDA meeting expected in Q2 2026
• Company plans to request End of Phase 2 meeting with FDA to review OST-503 non-small cell lung cancer frontline trial results in combination with Keytruda®

New York, New York--(Newsfile Corp. - January 5, 2026) - OS Therapies Inc. (NYSE American: OSTX) ("OS Therapies" or "the Company"), the world leader in listeria-based cancer immunotherapies, today provided stakeholders with a corporate outlook for the first half 2026.

The outlook highlights planned submissions to seek regulatory approval for the Company's lead candidate OST-HER2 in the U.S., U.K. and Europe, the expected release of Phase 2b biomarker data from the Company's Metastatic Osteosarcoma Program in the first half of January 2026, as well as additional pipeline and corporate milestones.

"OS Therapies is potentially at the cusp of improving the standard of care for patients with metastatic osteosarcoma," said Chairman & CEO Paul Romness. "2025 was a transformational year in which we announced promising OST-HER2 clinical trial results and had significant interactions with regulatory agencies in the U.S., U.K. and Europe regarding the path toward conditional marketing authorizations in 2026. We have incorporated the guidance received from those meetings into a clear regulatory plan that aligns our strategy with each regulatory agency's specific feedback."

Mr. Romness added, "In parallel, with much of the work related to OST-HER2 regulatory submissions winding down in the second half of Q1 2026, we expect to start making regulatory progress in our human OST-503 and OST-504 programs. We also look forward to completing a go-public transaction for our OS Animal Health subsidiary in the first half of 2026, with a confidential filing with the SEC expected in the very near future."

The Company expects to release biomarker data from its Phase 2b human clinical trial of OST-HER2 in the prevention or delay of recurrent, fully resected, pulmonary metastatic osteosarcoma during the week of the J.P. Morgan Healthcare Conference 2026.

The Company reiterates its intention to file a BLA with the U.S. FDA under the Accelerated Approval Program (Accelerated Approval) by the end of January 2026. The Company intends to complete MAA submissions seeking conditional marketing authorization with the U.K. MHRA and Europe's EMA by end of February 2026 and March 2026, respectively.
Following these submissions, the Company expects to engage in multiple meetings with regulatory authorities in the U.S., U.K., and Europe during the first half of 2026. These discussions are expected to address proposed surrogate clinical efficacy endpoints, confirmatory trial design, and post-market authorization monitoring plans in support of regulatory review. Following these additional meetings requested by the FDA, MHRA and EMA, the Company anticipates the potential to receive regulatory approval for OST-HER2 in the U.K. in Q2 2026, in the United States in Q3 2026 and in Europe by the end of Q4 2026.

OST-HER2 has received Orphan Disease Designation (ODD) and Fast Track Designation from the FDA and EMA, and has received Rare Pediatric Disease Designation (RPDD) from FDA. Under the RPDD program, if the Company receives Accelerated Approval prior to September 30, 2026, it will become eligible to receive a Priority Review Voucher (PRV) that it intends to sell. The most recent PRV sale valued at $160 million occurred in June 2025.

The Company expects to advance a go-public transaction for its OS Animal Health subsidiary, with a confidential filing with the U.S. Securities and Exchange Commission expected in early January 2026. OS Animal Health is seeking to gain regulatory approval for OST-HER2 from the United States Department of Agriculture (USDA) for the treatment of pulmonary metastatic osteosarcoma, as well as frontline osteosarcoma. OST-HER2 was featured in the Emmy-nominated documentary 'Shelter Me: Cancer Pioneers' streaming on PBS.

Beyond OST-HER2, the Company expects to advance additional human oncology programs. The Company expects delayed data from its OST-504 Phase 1 trial in castration resistant prostate cancer in the first quarter of 2026 after prioritizing biomarker lab partner resources for osteosarcoma data analysis, with an End of Phase 1 meeting with the FDA expected in Q2 2026. The Company also expects an End of Phase 2 meeting with the FDA in the Q2 2026 to review OST-503 non-small cell lung cancer frontline trial results in combination with Keytruda®.

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. The Company is the world leader in listeria-based cancer immunotherapies. OST-HER2, the Company's lead asset, is an immunotherapy designed to leverage the immune-stimulatory effects of Listeria bacteria to generate a strong immune response targeting the HER2 protein. OST-HER2 has received Rare Pediatric Disease Designation from the U.S. Food & Drug Administration and has also received Fast Track and orphan drug designations from the U.S. FDA and European Medicines Agency in Europe. The Company reported positive data in its Phase 2b clinical trial of OST-HER2 in recurrent, fully resected, lung metastatic osteosarcoma, demonstrating a statistically significant benefit in the study's primary endpoint of 12-month event free survival (EFS) primary endpoint of the study as well as 2-year overall survival data, the study's secondary endpoint. The Company anticipates submitting a Biologics License Application (BLA) to the U.S. FDA for OST-HER2 in osteosarcoma in 2026 and, if approved prior to September 30, 2026, would become eligible to receive a Priority Review Voucher that it intends to sell. OST-HER2 has also completed a Phase 1 clinical study primarily in breast cancer patients and has demonstrated preclinical efficacy in multiple models of breast cancer. In veterinary oncology, 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) platform, known as its tunable ADC (tADC) platform, which is designed to create tunable antibody-linker-payload candidates. This platform leverages the Company's proprietary Si-Linker and Conditionally Active Payload (CAP) technology designed to enable 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 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.

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