EMA Initiates Rolling Review of OS Therapies' OST-HER2 for Osteosarcoma

The European Medicines Agency has initiated a rolling review of OS Therapies' OST-HER2 conditional marketing authorization request for preventing recurrence in fully resected, pulmonary metastatic osteosarcoma. The company's stock surged 12.4% over the past week, bringing its market capitalization to $68.5 million.

The EMA's Committee for Advanced Therapy, in conjunction with the Committee for Medicinal Products for Human Use and Pharmacovigilance Risk Assessment Committee, has initiated Continuous Evaluation ("Rolling Review") of the OST-HER2 Conditional Marketing Authorisation (CMA) request regulatory dossier. OS Therapies and EMA have agreed that 3-year overall survival data will serve as the basis to complete evaluation of the CMA request. The company has aligned with both EMA and Australia's Therapeutic Goods Administration on using 3-year overall survival as the approvable clinical efficacy endpoint for conditional marketing authorizations.

OS Therapies submitted 2-year overall survival data, with EMA requesting updated 2.5-year overall survival data that will be available by the middle of the second quarter of 2026, and 3-year overall survival data that will become available early in the fourth quarter of 2026. The company anticipates a potential CMA decision by EMA in the fourth quarter of 2026.

Alignment has also been achieved with EMA and TGA on seroconversion data serving as surrogate clinical efficacy data to support CMAs for early market access and eligibility for a Priority Review Voucher under Rare Pediatric Disease Designation. Alignment was achieved on non-clinical, CMC and safety data, and on existing drug product being used to initiate Phase 3.

OS Therapies plans to initiate a confirmatory Phase 3 trial in Australia in the third quarter of 2026. The company anticipates receiving a Biologics License Application from the U.S. FDA for OST-HER2 in osteosarcoma in 2026. The company is seeking a BLA under the Accelerated Approval Program in the U.S. and conditional MAAs in the U.K. and Europe, which all require confirmatory studies to be initiated prior to approval.

EMA selected the company into its Raw Data Pilot program. OST-HER2 was granted Advanced Therapy Medicinal Product designation by the U.K. Medicines and Healthcare products Regulatory Agency. OST-HER2 has received orphan drug designation, fast track designation and rare pediatric disease designation from the FDA.

The company forecasts European peak OST-HER2 osteosarcoma sales exceeding $300 million following the ATMP designation, with over $50 million in sales expected in 2027. Under the RPDD program, if the company receives Accelerated Approval in the United States, it will become eligible to receive a Priority Review Voucher that it intends to sell. The most recent publicly disclosed PRV transaction occurred in January 2026 at a reported value of $100 million.

Upcoming U.S. FDA and U.K. MHRA meetings are scheduled in the second quarter of 2026. Market access interactions related to reimbursement with the UK's NICE and EMA Health Technology Assessment processes have commenced simultaneously. International regulatory coordination has also commenced under the EMA FDA Information Sharing programme.

The company also announced it expanded OST-503 Phase 2 candidate indications to include pancreatic cancer alongside non-small cell lung cancer, following review of target vector antigens that include all KRAS G12 position mutations, which represent 76% of all KRAS mutations in cancer.