OST-HER2 2.5-Year OS Data Drives FDA Type C Meeting

For biotech and pharma investors, OST-HER2's regulatory story hinges on a single statistical design decision: whether the FDA will accept pooled non-concurrent historical controls or demand concurrent natural history data from OST-400. The Type C meeting, set for mid-September after the 3-year survival readout, will also determine whether RMAT designation and rolling review are attainable. A favorable decision could position a gene-edited Listeria-based immunotherapy for a faster BLA path, while rejection would force costly trial redesign.

OS Therapies, Inc. announced on August 13, 2026 that the U.S. Food and Drug Administration has granted its requested Type C Statistical Methods meeting to review 2.5-year overall survival data from the Phase 2b trial of OST-HER2 in fully resected, pulmonary metastatic osteosarcoma. The company expects that meeting to take place in mid-September 2026 with the Center for Biologics Evaluation and Research, the FDA center responsible for gene-edited products. The announcement, distributed by Newsfile and syndicated across financial and general news outlets, is a company release rather than independent regulatory confirmation, so all milestones and survival claims should be treated as company-reported until corroborated.

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For biotech and pharma investors, OST-HER2's regulatory story hinges on a single statistical design decision: whether the FDA will accept pooled non-concurrent historical controls or demand concurrent natural history data from OST-400.

OST-HER2 is a gene-edited Listeria-based cancer immunotherapy that targets HER2, an antigen expressed in osteosarcoma. The Phase 2b trial enrolled patients whose pulmonary metastases were fully resected but who remained at high risk of recurrence; the goal is to prevent or delay that recurrence. The company stated that a sustained overall survival benefit was observed between the 2-year and 2.5-year timepoints, but it did not disclose hazard ratios, survival percentages, or confidence intervals. The upcoming interim 3-year overall survival data, expected in early September 2026, will be the first major readout before the FDA meeting and will likely influence the statistical discussion.

The central regulatory question is whether pooled non-concurrent published historical control data can serve as an appropriate comparator to evaluate OST-HER2 efficacy, or whether the FDA will require concurrent natural history data generated by the company's OST-400 study. According to Dr. Craig Eagle, Chief Medical Advisor at OS Therapies, the meeting will focus on "the appropriateness of using pooled non-concurrent published historical control data, as compared with concurrent natural history data generated via OST-400, to evaluate the clinical efficacy data generated from the OST-HER2 Metastatic Osteosarcoma Trial." That distinction matters because osteosarcoma is rare and a randomized placebo-controlled trial may be impractical or ethically difficult; however, historical controls can introduce selection bias, era effects, and endpoint inconsistency. If CBER signals openness to historical comparators, it could accelerate development and reduce costs, but if the agency demands concurrent controls, the path to approval becomes longer.

Beyond the statistical design, the company expects decisions after the meeting on the appropriate comparator arm, RMAT designation, and rolling review. RMAT, or Regenerative Medicine Advanced Therapy, designation would provide enhanced interactions and possible priority review for a cell-based or gene-edited product, while rolling review would allow submission of completed portions of a Biologics License Application. In parallel, the FDA's Center for Drug Evaluation and Research Biomarker Qualification Program is scheduling a separate Biomarker Data Review Meeting, and the MHRA is holding its own Scientific Advice Meeting to support a Conditional Marketing Authorisation Application, including whether the company can finalize its UK submission using 2.5-year overall survival data. This is a coordinated multi-agency push, but each pathway remains conditional on statistical acceptability.