OS Therapies Announces Overall and Event Free Survival Key Subgroup Data for OST-HER2 in Recurrent, Fully Resected, Pulmonary Metastatic Osteosarcoma

New York, New York--(Newsfile Corp. - October 22, 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 additional overall and event free survival data generated from the Company's 41-patient Phase 2b clinical trial of its off-the-shelf immunotherapeutic candidate OST-HER2 in recurrent, fully resected, pulmonary metastatic osteosarcoma (the "Phase 2b Osteosarcoma Trial"). The Company previously announced statistically significant positive final 2-year overall survival data from its Phase 2b Osteosarcoma Trial on October 10, 2025. The Company performed these subgroup analyses following its participation in the October 10, 2025 FDA/The Osteosarcoma Institute (OSI) Workshop: Advancing Osteosarcoma Drug Development - Connecting Research and Regulatory Pathways for Improved Outcomes.

• Patients with a lung-only second or greater metastatic event:
  • 2-year Overall Survival: 80.0% (8/10, 2 lost to follow-up)
  • 1-year Event Free Survival: 50% (6/12, 0 lost to follow-up)
• Patients with a lung-only first metastatic event:
  • 2-year Overall Survival: 73.8% (19/26, 3 lost to follow-up) vs. 30% Natural History Comparator (p < 0.0001)^[1]
  • 1-year Event Free Survival: 28.6% (8/28, 1 Lost to follow-up)

"There was significant interest in the different patient subgroups that made up our study given the challenges typically seen in recruiting for clinical trials in osteosarcoma, especially with patients' first metastatic event for which we have sufficient data to perform this subgroup analysis," said Paul Romness, MPH, Chairman & CEO of OS Therapies. "We believe the favorable safety profile when compared with alternative institutional standards of care that rely primarily on chemotherapeutic agents played a significant role in that. The recruitment of patients into our study seems representative of the overall annual patient population and the overall survival efficacy signal appears broadly across the different subgroups of patients in our trial."