OST-HER2 (AOST-2121)

June 30, 2026: OS Therapies, Inc. (NYSE: OSTX) provided an FDA regulatory update for its planned Biologics License Application (BLA) under Accelerated Approval for OST-HER2 to prevent or delay recurrence in fully resected, pulmonary metastatic osteosarcoma. The company requested a Type B FDA meeting to review its 2.5-year overall survival (OS) data and to confirm that 3-year OS is an approvable clinical efficacy endpoint; it said it has already aligned with the MHRA and EMA on using 3-year OS to support Conditional Marketing Authorisations, and that FDA/EMA have begun joint coordination on the OST-HER2 dossier.

OS Therapies also submitted pharmacodynamic response biomarker data to the FDA BEST program to evaluate as surrogate clinical efficacy data. At the Type B meeting, it plans to discuss adding OST-400 (a retrospective natural history study database) as an additional synthetic control comparator arm, alongside pooled historical control data previously shared with FDA, and to review statistical analysis methods for the upcoming 3-year OS readout expected early in the fall. The company also expects to discuss outstanding Rolling Review, RMAT, and Breakthrough Therapy designation requests. It reiterated it is seeking a U.S. BLA for OST-HER2 in 2026 and anticipates UK/EMA conditional filings in 2026.