OS Therapies Begins FDA Filing for Experimental Cancer Treatment Aimed at Osteosarcoma Recurrence

OS Therapies Inc. (NYSE:OSTX) ("OS Therapies" or "the Company"), the world leader in listeria-based cancer immunotherapies, today announced that it has formally initiated a Biologics License Application (BLA) submission to the U.S. Food & Drug Administration (FDA) for OST-HER2 in the prevention or delay of recurrent, fully resected, pulmonary metastatic osteosarcoma ("Human Metastatic Osteosarcoma"). The Company has submitted the Non-Clinical and the Chemistry, Manufacturing, and Controls (CMC) modules of the BLA to FDA, along with a request for Rolling Review. At FDA's invitation following a December 2025 Type C Meeting, the Company has requested a Type D Meeting to review new Comparative Oncology OST-HER2 biomarker data generated from the Company's Phase 2b human clinical trial in Human Metastatic Osteosarcoma and a similar trial of OST-HER2 in spontaneous osteosarcoma in canines (the "OST-HER2 Comparative Oncology Data"). The Company expects to submit the clinical BLA module that will rely upon the OST-HER2 Comparative Oncology Data by the end of March 2026, keeping it on schedule to be eligible to receive approval by September 30, 2026.

"We are delighted in the FDA's interest in reviewing OST-HER2 Comparative Oncology Data," said Paul Romness, MPH, Chairman & CEO of OS Therapies. "There is strong demand for compassionate use of OST-HER2 from the patient community, underscoring the urgent need for new therapies in Human Metastatic Osteosarcoma. We remain committed to bringing OST-HER2 to market as expeditiously as possible and are grateful for FDA's engagement as we finalize the biomarker data package that will be submitted as part of Type D meeting preparations to support our request for a BLA under the Accelerated Approval Program."

Concurrent with this announcement, the Company announced it has updated its Regenerative Medicine Advanced Therapy (RMAT) designation requests to FDA with recent biomarker data. RMAT designation typically shortens the timeframe granted for review of a BLA submission significantly from the standard timelines, expediting the time to patient access.

OST-HER2 has received FDA Orphan Disease Designation (ODD) and Fast Track Designation from FDA & EMA and has received Rare Pediatric Disease Designation (RPDD) from FDA. Under the RPDD program, if the Company receives Accelerated Approval prior to September 30, 2026, it will become eligible to receive a Priority Review Voucher (PRV) that it intends to sell. The most recent PRV sale, valued at $200 million, occurred in January 2026.