MHRA agreed that the use of comparable historical control data – derived from a systematic evaluation of all suitable available peer-reviewed literature by independent biostatistics advisors presented in its most recent Scientific Advice Meeting (SAM) - was appropriate in the orphan indication Prevention or Delay of Recurrence in Fully Resected, Pulmonary Metastatic Osteosarcoma. Further, the Company achieved full alignment on the proposed design of its upcoming confirmatory Phase 3 trial design – including the proportion of patients to be dosed with remaining Phase 2 drug product versus forthcoming Phase 3 material. The Phase 3 trial is required to have commenced prior to being granted a CMAA. OS Therapies expects to complete the CMAA submission in the coming weeks. The Company also intends to commence the confirmatory Phase 3 as soon as possible in the fourth quarter of 2026 and site outreach has commenced accordingly.

The MHRA's supportive advice aligns with the Agency's recently published Rare Disease Regulatory Framework (https://www.gov.uk/government/consultations/draft-rare-disease-therapies-regulatory-framework/draft-rare-disease-therapies-regulatory-framework); and advice from the European Medicines Agency (EMA) pertaining to a forthcoming CMAA via the pan-European Centralised Procedure.

"Achieving full alignment with MHRA and EMA, which paves the way for our upcoming CMAA submissions, and the initiation of our confirmatory Phase 3 trial is a major achievement," said Paul Romness, MPH, Chairman & CEO of OS Therapies. "With this full alignment now in hand, and with it the recognition from international regulators that the standard of care in Osteosarcoma has not meaningfully changed in the last forty years, we are bringing this to the U.S. Food & Drug Administration (FDA). The FDA is part of the Orbis Project that coordinates approvals between international regulators, including the UK. The FDA is considering the ongoing Biologics License Application (BLA) submission that began in January 2026, with potential early market access under the Accelerated Approval Program. Additionally, the EMA recently informed the Company that a previously requested SAWP meeting was no longer required prior to submission of the CMAA to EMA."

OST-HER2 has received Orphan Drug Designation (ODD), Fast Track Designation (FTD) and Rare Pediatric Disease Designation (RPDD) from the FDA, and ODD, FTD and Advanced Therapy Medicinal Products (ATMP – RMAT equivalent in the EU and UK) from the EMA and MHRA. Under the RPDD program, if the Company is granted a BLA in the United States, it will become eligible to receive a Priority Review Voucher (PRV) that it intends to sell. The most recent PRV sale occurred in August 2026 for $220 million. However, there can be no assurance that the Company would realize a comparable value, if any, in connection with any future PRV sale. OS Therapies has completed resubmission of a Regenerative Medicine Advanced Therapy (RMAT) request and the Company's Commissioner's National Priority Review Voucher (CNPV) letter of intent has been accepted by FDA. The Company intends to request Rolling Review of the ongoing BLA submission that began in January 2026 following its upcoming mid-September 2026 FDA Type C Statistical Methods Meeting. OS Therapies is seeking to obtain a BLA under the Accelerated Approval Program in the U.S. and Conditional Marketing Authorization Applications (CMAAs) in Europe, the U.K. and Australia for OST-HER2 in metastatic osteosarcoma in the fourth quarter of 2026.