OS Therapies, Inc. (OSTX) said the European Medicines Agency has initiated a rolling review of its Conditional Marketing Authorization (CMA) application for OST-HER2, an immunotherapy designed to prevent or delay recurrence in patients with fully resected pulmonary metastatic osteosarcoma. The company called the regulatory progress a major step toward potential early market access in Europe.
Pulmonary metastatic osteosarcoma is an aggressive form of bone cancer that often spreads to the lungs, where recurrence after surgery remains a significant clinical challenge. OST-HER2 is a gene-edited, listeria-based cancer immunotherapy engineered to stimulate a targeted immune response against HER2-expressing tumor cells.
Regulatory Alignment and Review Pathway
According to OS Therapies, regulators at both the EMA and Australia's Therapeutic Goods Administration (TGA) have aligned on three-year overall survival as the approvable clinical efficacy endpoint for conditional approvals. The agencies also agreed that seroconversion biomarker data may serve as surrogate evidence to support early authorization and potential eligibility for a Priority Review Voucher under the Rare Pediatric Disease Designation.
The EMA additionally selected OS Therapies for its Raw Data Pilot Program, and the UK MHRA has granted OST-HER2 Advanced Therapy Medicinal Product (ATMP) designation.
Next Steps and Upcoming Milestones
A confirmatory Phase 3 trial is planned to begin in Australia in the third quarter of 2026 to meet global regulatory requirements. OS Therapies also has upcoming meetings with both the U.S. FDA and UK MHRA in the second quarter of 2026 to further define the development and approval pathway.
Beyond OST-HER2 the company is advancing additional pipeline programs:
-OST-504 : Phase 1b biomarker analysis in castration-resistant prostate cancer -OST-503 : Phase 2 program expanded to include pancreatic cancer, targeting KRAS G12 mutations, which represent 76% of all KRAS-mutated cancers.
OS Therapies forecasts European peak sales for OST-HER2 exceeding $300 million with more than $50 million expected in 2027 following ATMP designation.
OSTX has traded between $1.15 and $2.57 over the past year. The stock is currently trading at $1.76, up 7.99%.
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April 24, 2026 15:15 ET Economics news flow was relatively light this week even as the conflict in the Middle East continued, raising concerns for policymakers. In the U.S., spending data, initial jobless claims and pending home sales were the highlights. Business confidence in the biggest euro area economy was in focus in Europe. Inflation data from Japan gained attention in Asia.