OS Therapies Inc (NYSE-A:OSTX) shares jumped 12.4% following favorable feedback from the FDA regarding its OST-HER2 treatment for osteosarcoma.
The clinical-stage biopharmaceutical company announced it received positive written input from a mid-June FDA Type D Meeting concerning the endpoints needed to support an Accelerated Approval Program marketing application for its Phase 2b trial. This trial evaluates OST-HER2’s ability to prevent or delay recurrence in pediatric patients with fully resected lung metastatic osteosarcoma.
In response to the feedback, OS Therapies has submitted requests for an End of Phase 2 Meeting and Breakthrough Therapy Designation with the FDA. The End of Phase 2 Meeting is anticipated in Q3 2025.
Dr. Robert Petit, Chief Medical & Scientific Officer at OS Therapies, noted the FDA’s guidance on the use of external control comparators in scenarios where placebo-controlled randomized trials are impractical, especially in rare pediatric diseases. The agency also recommended statistical approaches to compare OST-HER2 treatment against external control arms to support a Biologics Licensing Application.
OST-HER2 has received Rare Pediatric Disease Designation for osteosarcoma from the FDA. If granted conditional BLA approval through Accelerated Review before September 30, 2026, the therapy would qualify for a Priority Review Voucher (PRV), which OS Therapies plans to sell immediately. The most recent PRV sale fetched $160 million in June 2025.
The company estimates the market opportunity for OST-HER2 in preventing lung metastases exceeds $500 million, within the broader osteosarcoma treatment market valued at $1.2 billion in 2022, according to Data Bridge Market Research.