BLA Submission to FDA Underway for Metastatic Osteosarcoma Treatment

Developers have initiated a biologics license application (BLA) submission to the FDA for OST-HER2 to prevent recurrent, fully resected, pulmonary metastatic osteosarcoma, according to a press release from OS Therapies.¹

The application is based on results from a phase 2b trial (NCT04974008).² In December 2025, a Type C meeting was held, and OS Therapies requested a Type D meeting to review the Comparative Oncology OST-HER2 biomarker data. The complete BLA will rely on the OST-HER2 Comparative Oncology Data and will be submitted by the end of March 2026. This would allow the treatment to be approved by September 30, 2026.

Additionally, developers have updated the regenerative medicine advanced therapy designation request based on recent data. This request helps to shorten the timeframe and grants review of the BLA submission in a timelier fashion.

"We are delighted in the FDA’s interest in reviewing OST-HER2 Comparative Oncology Data," Paul Romness, MPH, chairman and chief executive officer of OS Therapies, said in the press release.¹ “There is strong demand for compassionate use of OST-HER2 from the patient community, underscoring the urgent need for new therapies in human metastatic osteosarcoma. We remain committed to bringing OST-HER2 to market as expeditiously as possible and are grateful for FDA’s engagement as we finalize the biomarker data package that will be submitted as part of Type D meeting preparations to support our request for a BLA under the accelerated approval program.”

In previously reported data, OST-HER2 had a 12-month event-free survival (EFS) rate of 33% vs 20% among historical controls (P = .0158).³ The 1-year overall survival (OS) rates were 91% with OST-HER2 vs 80% with the historical control (P = .0700). The OS rates at 2 years were 61% and 40% (P = .0576).

In a post hoc analysis, the 12-month EFS rate for patients who were female was 47% compared with 20% in those who were male (P = .0604). For those who had 1 prior resection, the 12-month EFS rate was 25%; for those with 2 or more prior therapies, it was 55% (P = .1366).

The median time to recurrence among those who did not achieve 12-month EFS was 5.9 months and 4.7 months for those in the non-concurrent control group (P = .1454).

A total of 39 patients between the ages of 12 and 39 were enrolled. Patients were given OST-HER2 every 3 weeks for 48 weeks with 4 doses constituting 1 treatment cycle every 12 weeks per cycle. OST-HER2 was given at 1 x 10⁹CFU until week 48 or until progressive disease, intolerably toxicity, or other treatment discontinuation criteria were met.⁴

The primary end point was the number of patients who achieved EFS at 12 months vs historical controls. An examination for recurrences occurred every 3 months, which was consistent with standard of care. The secondary end point was 3-year OS vs historical controls.

Previously, the FDA granted orphan disease designation and fast track designation to OST-HER2. The European Medicines Agency has also granted similar designations. Additionally, the FDA has granted rare pediatric disease designation, and if the treatment receives accelerated approval prior to September 30, 2026, it will become eligible to receive a priority review voucher.

References

1. OS Therapies initiates US FDA BLA filing for OST-HER2 in the prevention or delay of recurrent, fully resected, pulmonary metastatic osteosarcoma. News release. February 2, 2026. Accessed February 2, 2026. https://tinyurl.com/855zdjyu
2. OS Therapies announces phase 2b clinical trial of OST-HER2 achieves primary endpoint with statistical significance in the prevention of recurrent, fully resected, lung metastatic osteosarcoma. News release. January 15, 2025. Accessed February 2, 2026. https://tinyurl.com/2tu9e5zb
3. Lagmay JP, Krailo MD, Dang H, et al. Outcome of patients with recurrent osteosarcoma enrolled in seven phase II trials through Children’s Cancer Group, Pediatric Oncology Group, and Children’s Oncology Group: learning from the past to move forward. J Clin Oncol. 2016;34(25):3031-3038. doi:10.1200/JCO.2015.65.5381
4. Osteosarcoma maintenance therapy with OST31-164 (OST-164-01). ClinicalTrials.gov. Updated January 22, 2025. Accessed February 2, 2026. https://clinicaltrials.gov/study/NCT04974008