OS Therapies, Inc., a Rockville, Maryland- and New York-based clinical-stage oncology company, announced on September 17, 2026 that it has achieved incremental alignment with the FDA on the adaptive design for the pending Phase 3 trial of OST-HER2 — its lead gene-edited, Listeria-based immunotherapy — in fully-resected, pulmonary metastatic osteosarcoma, matching the design already agreed with the U.K.’s Medicines and Healthcare products Regulatory Agency (MHRA) and the European Medicines Agency (EMA).
Chairman and CEO Paul Romness, MPH, said: “With alignment in hand with FDA on the most recent updates to the proposed adaptive design for the Phase 3 trial design reviewed with MHRA and EMA, we have overcome the key hurdle to initiating the Phase 3 in the U.K. and beyond. More importantly, now that MHRA has stepped up and volunteered to take the international lead with Project Orbis, we expect to be able to move expeditiously through the regulatory process in the U.K., U.S. and Europe.”
A Faster, More Coordinated Path Across Three Regulators
The Phase 3 trial is expected to begin in Q4 2026. Separately, following a successful Statistical Methods Scientific Advice Meeting, OS Therapies accepted MHRA’s request to serve as the company’s sponsor into Project Orbis — an FDA-launched initiative enabling simultaneous submission and review of oncology therapies across multiple countries’ regulators, aimed at giving cancer patients faster access to promising treatments. The FDA’s Center for Biologics Evaluation and Research (CBER) recently reopened Project Orbis specifically to foreign-sponsored U.S. companies. OS Therapies also expects to hold its previously disclosed Type B Pre-BLA meeting with the FDA in Q4 2026, following submission of the clinical section — including 3-year overall survival data — which would complete the BLA (Biologics License Application) filing it initiated in January 2026.
A Stack of Regulatory Designations, and a Valuable Voucher on the Table
OST-HER2 already holds Orphan Drug, Fast Track, and Rare Pediatric Disease designations from the FDA, plus Orphan Drug, Fast Track, and Advanced Therapy Medicinal Product status from the EMA. Under the Rare Pediatric Disease Designation program, a U.S. BLA approval would make OS Therapies eligible for a Priority Review Voucher (PRV) — a transferable credit the company intends to sell; the most recent PRV sale in the market went for $220 million in August 2026, though the release cautions there’s no guarantee OS Therapies would realize a comparable value in any future sale. The company has also resubmitted a Regenerative Medicine Advanced Therapy (RMAT) request, and the FDA has accepted its Commissioner’s National Priority Review Voucher (CNPV) letter of intent. OS Therapies is targeting a U.S. BLA under the Accelerated Approval Program, alongside Conditional Marketing Authorization Applications in Europe, the U.K., and Australia, in Q4 2026.
About OS Therapies
OS Therapies is a clinical stage oncology company focused on the identification, development, and commercialization of treatments for Osteosarcoma (OS) and other solid tumors. The Company is the world leader in gene-edited, Listeria-based cancer immunotherapies. OST-HER2, the Company’s lead asset, is an immunotherapy leveraging the immune-stimulatory effects of Listeria bacteria to initiate a strong immune response targeting the HER2 protein. OST-HER2 is designed to target two mutated extracellular epitopes and one mutated intracellular epitope of the HER2 oncogene, requiring only one of these three epitopes to be present in a tumor (or micro-metastasis) to trigger the desired immune response. OST-HER2 has received Orphan Drug Designation (ODD), Fast Track Designation (FTD) and Rare Pediatric Disease Designation (RPDD) from the U.S. Food & Drug Administration and has received ODD, FTD and Advanced Therapy Medicinal Products (ATMP) from the European Medicines Agency.
In addition, OS Therapies is advancing its next-generation Antibody Drug Conjugate (ADC) and Drug Conjugates (DC), known as tunable ADC (tADC), which features tunable, tailored antibody-linker-payload candidates. This platform leverages the Company’s proprietary silicon Si-Linker and Conditionally Active Payload (CAP) technology, enabling the delivery of multiple payloads per linker. For more information, please visit www.ostherapies.com.
