OS Therapies Inc (NYSE-A: OSTX), a clinical-stage biotechnology company focused on immunotherapies and targeted drug conjugates for cancer treatment, on Wednesday reported positive results from its Phase 2b clinical trial of OST-HER2 (OST31-164), an immunotherapy targeting HER2 for the prevention of recurrent, fully resected lung metastatic osteosarcoma.

The trial demonstrated a statistically significant 33.3% Event-Free Survival (EFS) at 12 months for OST-HER2-treated patients, compared to 20% in the historical control group (p = 0.0158). Further interim analyses show strong trends in favor of OST-HER2 for overall survival (OS), with 91% surviving at 1 year and 61% at 2 years.

Notably, all patients who achieved the 12-month EFS remain alive in follow-up. The treatment was well tolerated and safe. OST-HER2 is being developed for a rare paediatric cancer indication, osteosarcoma, with no currently approved treatments for this condition. The treatment leverages a bioengineered form of Listeria monocytogenes to stimulate a strong immune response against cancer cells expressing HER2.

OST-HER2 has received several designations from the FDA, including Rare Pediatric Disease Designation, and is expected to provide significant opportunities in the osteosarcoma market, estimated to be worth over USD500m in lung metastasis prevention alone. OS Therapies is also exploring the sale of a Priority Review Voucher (PRV), which could provide additional value for the company upon approval of OST-HER2.