OST-504 (ADXS-504)

May 18, 2026: OS Therapies, Inc. (NYSE: OSTX) reported Q1 2026 results and outlined upcoming regulatory and clinical catalysts for OST-HER2 in prevention/delay of recurrence in fully resected pulmonary metastatic osteosarcoma. The company said EMA and Australia’s TGA meetings aligned on use of an existing biomarker as a surrogate endpoint and on a confirmatory Phase 3 design with 3-year overall survival as the primary efficacy endpoint; EMA has initiated rolling review for a conditional MAA request. OS Therapies completed FDA submissions of clinical efficacy and biomarker data ahead of a Type B Pre-BLA meeting (upgraded from a Type D), and submitted non-clinical and CMC BLA modules with a request for rolling review; the company also submitted an RMAT request to FDA and noted ATMP designation from EMA and MHRA.

Upcoming milestones include release of 2.5-year overall survival data at ASCO 2026; completion of the OST-HER2 BLA filing and conditional MAA updates/filings (MHRA/EMA) incorporating the 2.5-year OS data; FDA Type B and MHRA scientific advice meetings on Phase 3 design; ATGA Clinical Trial Notification submission and Phase 3 initiation in Australia; and in 2H 2026, 3-year OS data plus FDA/EMA/MHRA/ATGA decisions on BLA/conditional MAAs.

Other catalysts: Phase 1b data expected from OST-503 in castration-resistant prostate cancer; and an S-1 filed for a proposed “go-public” transaction of OS Animal Health (timing pushed to 2H 2026) alongside a planned USDA regulatory meeting for canine osteosarcoma.