OS Therapies reports ‘positive’ results from Phase 2b trial of OST-HER2

OS Therapies (OSTX) announced positive 1-year event free survival, overall survival and safety clinical trial data updates from the 40 patient treatment arm of its Phase 2b clinical trial of immunotherapy candidate OST-HER2 in the prevention or delay of recurrence in fully resected, lung metastatic osteosarcoma. In data presented by Principal Investigator Dr. Damon Reed at the MIB Factor Osteosarcoma Conference held in Salt Lake City, Utah on Saturday June 28, 2025 the following data updates were released: 35% of OST-HER2-treated patients achieved 1-year event free survival compared with 20% of patients from peer-reviewed publication selected by Children’s Oncology Group as equivalent to osteosarcoma patient subpopulation enrolled; A total of 13 out of 40 patients were reported to have experienced severe adverse events during the trial, of which 7 patients’ adverse events were treatment-associated adverse events. All of the 7 patients’ TSAEs were grade 3 TSAEs; 0 patients experienced grade 4 or grade 5 TSAEs. None of the patients for whom TSAEs were reported discontinued the study. “The updated OST-HER2 data presented at MIB Factor that showed EFS data statistically significantly favoring OST-HER2 treated patients when compared with the leading peer-reviewed publications on historical event free survival outcomes in this subset of the pulmonary metastatic osteosarcoma patient population,” said Dr. Robert Petit, Chief Medical & Scientific Officer of OS Therapies. “The favorable safety profile of OST-HER2 compared with standard of care is also an important quality of life factor when assessing potential new treatment options for this difficult to treat patient population.”