NEW YORK, New York, April 30, 2026
OS Therapies announced that the European Medicines Agency (EMA) has initiated a rolling review of its Conditional Marketing Authorization (CMA) application for OST-HER2, an investigational listeria-based cancer immunotherapy designed to prevent or delay recurrence in fully resected pulmonary metastatic osteosarcoma. This regulatory milestone reflects strong global alignment with agencies including EMA and Australia’s TGA, validating the company’s strategy to accelerate early market access for rare pediatric cancers. OST-HER2 has already received Orphan Drug Designation (ODD), Fast Track Designation (FTD), and Rare Pediatric Disease Designation (RPDD), positioning it as a high-priority therapeutic candidate in oncology. The EMA has also selected OS Therapies for its Raw Data Pilot Program, further strengthening regulatory collaboration and data transparency.
Regulatory Alignment Strengthens Path to Early Approval
A critical breakthrough in the program is the agreement with EMA and TGA to use 3-year overall survival as the primary clinical endpoint for approval, while also recognizing immune biomarker seroconversion data as a surrogate efficacy indicator to support conditional approvals. This dual-approach significantly reduces development uncertainty and accelerates timelines for global regulatory filings across the U.S., Europe, U.K., and Australia.
The company plans to initiate a confirmatory Phase 3 trial in Q3 2026, starting in Australia, as required for full approval pathways. Additionally, ongoing coordination under the EMA-FDA information-sharing framework and upcoming regulatory meetings with the U.S. FDA and U.K. MHRA further reinforce the program’s global development momentum. The company anticipates a potential CMA decision by EMA in Q4 2026, aligning regulatory progress with commercial readiness.
OST-HER2 Demonstrates Strong Clinical and Commercial Potential
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OST-HER2 is a novel immunotherapy leveraging attenuated Listeria monocytogenes to stimulate a targeted immune response against HER2-expressing tumor cells, requiring only partial antigen expression to activate efficacy. The therapy has shown clinically meaningful benefits in Phase 2b trials, including improvements in event-free survival (EFS) and overall survival (OS) in osteosarcoma patients.
With regulatory alignment achieved across key areas including clinical, safety, CMC, and biomarker validation, OS Therapies is advancing toward accelerated approval pathways and early commercialization. The company forecasts peak European sales exceeding $300 million annually, with initial revenues potentially surpassing $50 million by 2027, highlighting strong market potential in a rare but high-need indication.
Pipeline Expansion and Platform Validation Across Oncology
Beyond osteosarcoma, OS Therapies is leveraging its listeria-based immunotherapy platform to expand into additional oncology indications. The company is advancing OST-504 in castration-resistant prostate cancer and OST-503 in non-small cell lung cancer (NSCLC), with expanded focus into pancreatic cancer targeting KRAS G12 mutations, which represent approximately 76% of KRAS-driven cancers.
These developments demonstrate the platform’s broad applicability across solid tumors, reinforcing its potential as a next-generation immunotherapy approach. The integration of biomarker-driven development strategies, including immune response profiling, further strengthens the company’s ability to deliver precision oncology solutions.
This milestone underscores a broader shift toward immunotherapy-driven cancer treatment, where targeted immune activation and biomarker-guided development are redefining clinical success. With strong regulatory backing, expanding pipeline potential, and promising clinical data, OS Therapies is positioning OST-HER2 as a transformative treatment option for patients with osteosarcoma, a rare and aggressive cancer with limited therapeutic options.
Source: OS Therapies press release
