OST-504

March 31, 2026 — OS Therapies, Inc. (NYSE: OSTX) announced it completed submission of clinical and immune-biomarker data from its Phase 2b trial of OST-HER2 (a listeria-based HER2-targeting immunotherapy) to the U.S. FDA ahead of a planned Pre-BLA meeting expected in May 2026. The company said a December 2025 FDA Type C meeting confirmed that the pre-specified immune biomarker strategy is suitable to serve as a surrogate efficacy endpoint to support a potential Biologics License Application (BLA) under the Accelerated Approval pathway, and that clinical outcomes correlate with the biomarker signature.

OS Therapies reported Phase 2b results showing statistically significant benefit on the 12-month event-free survival (primary endpoint) and overall survival (secondary endpoint), including a reported 75% 2-year overall survival (October 2025 update). It plans regulatory interactions with FDA/EMA/MHRA in 2Q 2026, initiation of a confirmatory Phase 3 trial in Australia in 3Q 2026, and targets U.S. accelerated approval and EU/UK conditional authorizations in 2H 2026.

Financially, 2025 net operating loss was $28.75M (vs. $8.82M in 2024); net loss per share was $0.98.