OS Therapies Achieves Global Regulatory Alignment on Phase 3 Trial Design for OST-HER2 in Osteosarcoma

OS Therapies has achieved global regulatory alignment on the design of its pending Phase 3 study of OST-HER2 in fully resected, pulmonary metastatic osteosarcoma, with the U.S. Food & Drug Administration (FDA) and the U.K. Medicines and Healthcare products Regulatory Agency (MHRA). A confirmatory Phase 3 study is required to have commenced prior to the grant of a Biologics License Application (BLA) under the Accelerated Approval Program in the U.S. and Conditional Marketing Authorisation Applications (CMAAs) in the U.K., Europe and Australia.

The patent-pending pharmacodynamic response biomarker has been accepted as a surrogate clinical efficacy endpoint, and the TGA and MHRA agreed to allow utilization of remaining Phase 2b drug product for initiation of the confirmatory Phase 3. FDA and EMA fully aligned with the Company on Chemistry, Manufacturing and Controls (CMC), and a market access process has been initiated with UK NICE and EU JCA.

"This alignment amongst each of the four key regulatory agencies where we are seeking early market access allows us to move forward with confidence as we prepare the Clinical Trial Notification (CTN) scheme submission to the Australian Therapeutic Goods Administration (TGA) to gain authorization to initiate the Phase 3 study," said the Chief Medical Advisor of OS Therapies. "Australia has a very attractive R&D tax incentive program complementing the company's existing UK R&D tax credit strategy to incentivize the initiation of global clinical trials, allowing us to initiate the Phase 3 with minimal cost. MHRA and TGA are allowing us to initiate the Phase 3 trial with the same drug product used in the Phase 2b trial, positioning the Phase 3 trial to open in the third quarter of 2026. FDA, MHRA, EMA and TGA have now aligned with the Company on the CMC plan and potency assays for commercial drug product."

The Phase 3 study is expected to commence late in the third quarter in Australia, making the Company eligible for regulatory decisions in the fourth quarter. EMA has already begun rolling review of the regulatory dossier, and the Company expects decisions regarding rolling review and Regenerative Medicine Advanced Therapy (RMAT) designation in the United States following its upcoming Type B Pre-BLA Meeting after a successful Type C Phase 3 Design Meeting.

OST-HER2 has received Orphan Drug Designation (ODD), Fast Track Designation (FTD) and Rare Pediatric Disease Designation (RPDD) from the FDA, and ODD, FTD and Advanced Therapeutic Medicinal Product (ATMP) designation from the EMA and MHRA. Under the RPDD program, if the Company is granted a BLA in the United States, it will become eligible to receive a Priority Review Voucher (PRV) that it intends to sell.

Earlier this year, following the submission of the Non-Clinical and Chemistry, Manufacturing & Controls (CMC) modules of its BLA to the FDA at the end of January 2026, the Company anticipated releasing additional biomarker data from its Human Metastatic Osteosarcoma Program in the first quarter of 2026, intended to further characterize immune pathway activation and evaluate the relationship between biomarker expression and observed clinical outcomes. The Company expected to complete conditional MAA submissions to both the MHRA and the EMA by the end of the first quarter of 2026, and remained on track to submit the Clinical BLA module to the FDA following an anticipated Type D meeting in March 2026. The CEO said the Company had "nearly completed additional follow-on biomarker analyses designed to further elucidate the drug's treatment effect and its relationship to clinical outcomes."

U.S., U.K. and European osteosarcoma key opinion leaders are being assembled to review the clinical and biomarker data and provide input on proposed confirmatory trial designs. The Company is seeking a BLA under the Accelerated Approval Program in the U.S. and conditional MAAs in the U.K. and Europe, and anticipates initiating the confirmatory trial in the third quarter of 2026 with the opening of a single site that allows it to meet the Accelerated Approval statutory requirement, with broader site activation expected following regulatory approval.

The Company reported positive data in its Phase 2b clinical trial of OST-HER2 in recurrent, fully resected, lung metastatic osteosarcoma, demonstrating clinically significant benefit in the 12-month event free survival (EFS) primary endpoint of the study.

Additionally, the Company announced that Ayala Pharmaceuticals, Inc. is dissolving. OS Therapies acquired all listeria-based clinical, pre-clinical and intellectual property assets from Ayala in April 2025, issuing 4.8 million shares of OS Therapies common stock that became eligible for trading on October 9, 2025. Ayala completed the liquidation of its OS Therapies common stock on February 9, 2026, and no longer holds any securities in the Company.