OS Therapies Provides Positive EMA Regulatory Update Following Positive Rapporteur Meeting

• Overall survival recognized as key efficacy endpoint in osteosarcoma, where no standard of care exists

• Rapporteur highlights potential broader benefits of OST-HER2 in pulmonary and primary osteosarcoma settings, supported by translational canine data from the University of Pennsylvania

New York, New York--(Newsfile Corp. - October 9, 2025) - OS Therapies Inc. (NYSE American: OSTX) ("OS Therapies" or "the Company"), a clinical-stage cancer immunotherapy and antibody drug conjugate biotechnology company, today announced a positive regulatory update following an October 6, 2025 meeting with its European Medicines Agency (EMA) rapporteur, the Dutch Medicines Evaluation Board (MEB).

During the meeting, OS Therapies and the Dutch Rapporteur aligned on key areas, including safety, non-clinical and chemistry, manufacturing, and controls (CMC) data in support of the Company's ongoing OST-HER2 Phase 2b clinical trial in the prevention or delay of recurrent, fully-resected, pulmonary metastatic osteosarcoma. The Rapporteur advised that the overall survival results, demonstrating statistically significant, final two-year data, may serve as an appropriate primary endpoint for consideration of conditional marketing authorization (CMA).

The meeting represented an important milestone toward formal EMA Scientific Advice, anticipated in December 2025. A potential pathway was also established to support a confirmatory, randomized clinical development program, which could explore additional osteosarcoma settings and potentially expand the product label upon full marketing authorization.

Meeting outcomes

• The safety profile from the Fully Resected Osteosarcoma clinical study was confirmed as positive. In addition, data from other Listeria monocytogenes candidates, representing more than 500 patients treated across four other therapeutic indications, may be sufficient to support a conditional marketing authorization (CMA).
• Non-clinical data is sufficient to support a CMA submission.
• The chemistry, manufacturing, and controls (CMC) data package was also viewed as sufficient to support a CMA.
• Efficacy data available as of July 2025 from the Fully Resected Osteosarcoma Trial were viewed as encouraging. The Rapporteur noted that 12-month Event-Free Survival (EFS) may not be the most appropriate endpoint and that overall survival (OS) could provide a stronger measure of clinical benefit, particularly if ongoing biomarker analyses confirm differential immune activation among patients showing favorable outcomes.
• The Rapporteur also indicated that efficacy data generated outside the Fully Resected Osteosarcoma Trial, such as in recurrent, unresectable, pulmonary metastatic osteosarcoma setting, could be incorporated into a post-market confirmatory clinical development program.

Additionally, the company is pleased to report that following the recently announced commencement of the Marketing Authorisation Application (MAA) submissions process with the UK MHRA, that the Agency has kindly granted OS Therapies an expedited Market Access Scientific Advice Meeting. This is an important milestone in the MAA submission and approval process. The meeting is intended to ensure alignment between Sponsors and the Agency on issues that will be evaluated during the MAA review process, with the intent of accelerating patient access.