OS Therapies announced it has received positive written feedback from the U.S. Food and Drug Administration (FDA) following a mid-June Type D meeting. The development supports its plan to use an external control arm to support a Biologics Licensing Application (BLA) for its lead candidate, OST-HER2, a Listeria monocytogenes-based immuno-oncology asset originally developed by Advaxis and fully acquired from Ayala Pharmaceuticals in April 2025.
The firm says the feedback provides clarity on the regulatory path for OST-HER2 in preventing recurrence in pediatric osteosarcoma, an ultra-rare indication where randomized, placebo-controlled trials are ethically and logistically unfeasible. According to the company, the FDA provided “collaborative input regarding suggested statistical methods” for comparing the Phase 2b trial data against historical controls, marking a step toward a potential accelerated approval.
Following the positive feedback, the company has submitted requests for an End-of-Phase-2 meeting, expected in Q3 2025, and for Breakthrough Therapy Designation (BTD). A rolling BLA submission is planned to commence following the meeting.
The regulatory momentum comes five months after OS Therapies reported positive Phase 2b results showing OST-HER2 achieved a 33.3% event-free survival rate at 12 months versus 20% for historical controls (p=0.0158) in 39 evaluable patients (from 41 enrolled) with recurrent, fully resected lung metastatic osteosarcoma. Interim overall survival analyses showed favorable trends with one-year overall survival (OS) of 91% versus 81% (p=0.0700) and 2-year OS of 61% vs 40% (p=0.0576), though not statistically significant.
The company’s approach differs significantly from previous HER2-targeted attempts in osteosarcoma, such as the Children’s Oncology Group’s Phase 2 trial of trastuzumab (NCT00023998), which showed no survival benefit between HER2-positive and negative patients. If OS Therapies secures accelerated approval before September 30, 2026, it would receive a Priority Review Voucher potentially worth $160 million based on the most recent sale by Bavarian Nordic in June 2025. The company will present additional data from its Phase 2b trial at the MIB Agents FACTOR conference in Salt Lake City on June 28, 2025, with management indicating sufficient cash runway into mid-2026 to complete the regulatory process.
Filed Under: Oncology
