OST-HER2 (AOST-2121)

September 2, 2026: OS Therapies (NYSE: OSTX) provided a regulatory and clinical update for OST-HER2 in prevention/delay of recurrence in fully resected pulmonary metastatic osteosarcoma. The company said interim 3-year overall survival data and U.S. FDA Type C Statistical Methods and U.K. MHRA Statistical Methods Scientific Advice meetings are expected in September 2026, with RMAT and Rolling Review decisions expected after the FDA meeting. Final 3-year overall survival data, an FDA pre-BLA meeting, BLA submission, and MHRA/EMA conditional marketing authorization submissions are expected in Q4 2026; a confirmatory Phase 3 clinical trial application is planned after the MHRA meeting for a Q4 2026 trial start.

The company said OST-HER2 previously showed positive Phase 2b data, including clinically significant benefit on the 12-month event-free survival primary endpoint and overall survival secondary endpoint. OST-HER2 has FDA Orphan Drug, Fast Track, and Rare Pediatric Disease designations, and EMA Orphan Drug, Fast Track, and ATMP status. OS Therapies said it has resubmitted an RMAT request and plans to seek accelerated approval in the U.S. plus conditional approvals in Europe, the U.K., and Australia in Q4 2026.

Separately, OS Animal Health requested a USDA meeting on reinstating conditional approval for OST-HER2 in canine osteosarcoma, expected in Q4 2026.