OST-HER2 (AOST-2121)

August 13, 2026: OS Therapies (NYSE: OSTX) said the FDA granted a Type C Statistical Methods meeting for OST-HER2 to review 2.5-year overall survival data from the Phase 2b trial in prevention of recurrence in fully resected, pulmonary metastatic osteosarcoma. The meeting is expected in mid-September 2026, alongside a pending FDA biomarker data review meeting. The company also said the U.K. MHRA granted a Scientific Advice Meeting, expected in September 2026, on statistical methods supporting a planned Conditional Marketing Authorisation Application.

The company said overall survival benefit was sustained from the 2-year to 2.5-year timepoints, and interim 3-year overall survival data are expected in early September 2026. OS Therapies said the FDA meeting should help determine the appropriate comparator arm for interpreting OST-HER2 efficacy, including pooled historical controls versus concurrent natural history data from OST-400.

OST-HER2 previously showed clinically significant benefit on the 12-month event-free survival primary endpoint and overall survival secondary endpoint in Phase 2b, according to the release. Following the upcoming meetings and 3-year data, the company expects decisions on its pending RMAT designation, FDA rolling review, and plans a potential accelerated-approval BLA by year-end 2026, plus conditional filings in Europe, the U.K., and Australia.