On June 24, 2025 OS Therapies (NYSE-A: OSTX) ("OS Therapies" or "the Company"), a clinical-stage immunotherapy and Antibody Drug Conjugate (ADC) biopharmaceutical company, reported that it received positive written feedback from the US Food & Drug Administration ("FDA") Type D Meeting that occurred in mid-June 2025 regarding endpoints required to support an Accelerated Approval Program marketing application for its Phase 2b trial of OST-HER2 in the prevention or delay of recurrence in fully resected, pediatric lung metastatic osteosarcoma (Press release, OS Therapies, JUN 24, 2025, View Source [SID1234654098]). The Company reiterates that additional data from its Phase 2b trial will be presented at the major osteosarcoma conference MIB Factor in Salt Lake City on Saturday June 28, 2025 at 3:30pm MDT.
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Concurrent with this announcement, the Company announced that it has submitted End of Phase 2 Meeting and Breakthrough Therapy Designation (BTD) requests to FDA based on the positive Type D Meeting feedback. The End of Phase 2 Meeting is expected to occur in the third quarter of 2025. This is in alignment with the company’s overall regulatory strategy and timelines.
"We are pleased with the feedback we received from the FDA regarding the use of external control comparators in settings where placebo-controlled randomization trials are not feasible – particularly in rare pediatric diseases such as the indication treated by OST-HER2 ," said Dr. Robert Petit, Chief Medical & Scientific Officer of OS Therapies. "Moreover, we received additional collaborative input regarding suggested statistical methods as we seek to compare OST-HER2 active treatment with external control arm(s) to support a Biologics Licensing Application (BLA) via the Accelerated Approval Program. Taken together, the feedback gives us insight on the FDA’s current position and allows us to be fully prepared for the End of Phase 2 Meeting."
OST-HER2 has received Rare Pediatric Disease Designation (RPDD) for osteosarcoma from the US FDA, and if it receives a conditional BLA via Accelerated Review prior to September 30, 2026, it will become eligible to receive a Priority Review Voucher (PRV) that it intends to immediately sell. The most recent PRV sale occurred in June 2025, valued at $160 million.
The osteosarcoma treatment market was estimated at $1.2 billion in 2022 according to Data Bridge Market Research. Approximately 50% of patients are diagnosed with a lung metastasis at some point following surgical resection and chemotherapy. 3-year survival rates in patients who were not diagnosed with a metastasis are 59%. 3-year survival rates in patients who were diagnosed with pulmonary metastasis were 30%. The Company believes the market opportunity for OST-HER2 in the prevention of lung metastases is over $500 million.
OST-HER2, an immunotherapy for osteosarcoma that uses a HER2-bioengineered form of the bacterium Listeria monocytogenes to trigger a strong immune response against HER2-expressing cancer cells, is featured in the movie Shelter Me: The Cancer Pioneers. The movie offers a look into canine comparative oncology, a field that compares treatment of cancers in dogs to those in people and covers developing treatments for rare forms of cancer. The movie is available via streaming on PBS’ website.