Confirmatory Phase 3 trial to commence prior to BLA grant under Accelerated Approval Program in the U.S. and Conditional MAA in the U.K., Europe and Australia Patent pending pharmacodynamic response biomarker accepted as surrogate clinical efficacy endpoint TGA and MHRA agree to allow utilization of remaining Phase 2b drug product for initiation of confirmatory Phase 3 FDA and EMA fully align with Company on Chemistry, Manufacturing and Controls (CMC) Market access process initiated with UK NICE and EU JCA New York, New York and Rockville, Maryland--(Newsfile Corp. - June 8, 2026) - OS Therapies, Inc. (NYSE American: OSTX) ("OS Therapies" or "the Company"), the world leader in gene-edited, Listeria-based cancer immunotherapies, today announced that it achieved alignment on the design of its pending Phase 3 study of OST-HER2 in the prevention or delay of recurrence in fully resected, pulmonary metastatic osteosarcoma with the U.S. Food & Drug Administration (FDA) and the U.K. Medicines and Healthcare products Regulatory Agency (MHRA). A confirmatory Phase 3 study is required to have commenced prior to the grant of a Biologics License Application (BLA) under the Accelerated Approval Program in the U.S. and Conditional Marketing Authorisation Applications (CMAAs) in the U.K., Europe and Australia.