OST-HER2 (AOST-2121)

October 6, 2026: OS Therapies (NYSE: OSTX) reported final 3-year overall survival data from its Phase 2b trial of OST-HER2 (daznelimgene lisbac; brand name accepted by WHO as Herlystic) in fully resected, pulmonary metastatic osteosarcoma. In 41 enrolled patients, 3-year overall survival was 72.7% versus 45.8% in a comparable combined published historical control (p=0.0006); four patients were lost to follow-up. The company also said the study previously showed clinically significant benefit on the 12-month event-free survival primary endpoint and overall survival secondary endpoint.

The company said it is preparing regulatory submissions for early market access in the U.S., U.K., Europe, and Australia. It plans to submit a CTA to the U.K. MHRA to start the confirmatory Phase 3 trial, which it said is required for FDA accelerated approval and conditional marketing applications with MHRA, EMA, and Australia’s TGA. OS Therapies intends to complete its U.S. BLA submission under Accelerated Approval and CMAA filings in Europe, the U.K., and Australia in Q4 2026.

OST-HER2 has FDA Orphan Drug, Fast Track, and Rare Pediatric Disease designations, plus EMA Orphan, PRIME, and ATMP designations.