FDA Type C Meeting Granted for Pulmonary Metastatic Osteosarcoma Therapy

The FDA has granted a Type C Statistical Methods meeting to OS Therapeutics in regard to the phase 2b trial (NCT04974008) assessing OST-HER2 and the 2.5-year overall survival (OS) results for patients with fully resected, pulmonary metastatic osteosarcoma.¹

The meeting is expected to be held in September 2026 and include members from the Center for Biologics Evaluation and Research. There is also a pending Biomarker Data Review Meeting being scheduled with participants of the Center for Drug Evaluation and Research’s Biomarker Qualification Program. Additionally, the 3-year OS data are expected to be announced in September.

Along with the FDA’s meeting, the UK Medicines and Healthcare products Regulatory Agency has granted a new Scientific Advice Meeting to review the statistical methods that will be used to support OS Therapeutics’ pending Conditional Marketing Authorisation Application submissions. This meeting will determine if the drug’s developer can finalize the UK decision and utilize the 2.5-year OS data. This meeting will also occur in September.

“We expect this Type C Statistics Methods Meeting with FDA to 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,” Craig Eagle, MD, chief medical advisor and member of the OS Therapies Board of Directors, said in the press release.¹ “We are heartened that OS at the 2.5-year timepoint remained unchanged from the 2-year timepoint. We look forward to the interim 3-year OS data in early September 2026, that will allow for decisions on our pending Regenerative Medicine Advanced Therapy (RMAT) designation submission, FDA Rolling Review and Commissioner’s National Priority Review Voucher more rapidly to facilitate a potential biologics license application under the Accelerated Approval Program by year end 2026.”

Previous Data Readouts for OST-HER

The 2.5-year OS rate was 75% with OST-HER2 vs 47% with pooled historical control (P = .003) compared with the 2-year OS rates of 75% vs 60% (P = .034).² For the 2- and 2.5-year data, there were no new patient deaths.

In August 2025, data regarding a small cohort of patients with recurrent, fully resected, pulmonary metastatic osteosarcoma were released.³ The 2-year OS rate was 66.6% for those who were given OST-HER2 vs 40% in the historical control cohort (P = .0046).

Furthermore, data from July 2025 showed that among 40 patients who were treated with OST-HER2, the 1-year event-free survival (EFS) rate was 35%.⁴

In January 2025, when the primary end point from the phase 2b trial was met in the lung-only cohort, the enrollment criteria included patients 12 to 39 years old who had recurred, fully resected lung only metastatic osteosarcoma.⁵ Additionally, 39 patients were to be enrolled across 21 centers in the single-arm study; patients were to spend 52 weeks on study, dosed 16 times every 3 weeks for 48 weeks, with a 4-week follow-up at the final visit. The 12-month EFS rate was 33% vs 20% with historical control (P = .0158). The interim analysis showed a 1-year OS rate of 91% vs 80% for historical control (P = .0700), and the 2-year OS was 61% vs 40% (P = .0576).

OST-HER2 Regulatory Actions

Previous regulatory actions for OST-HER2 include orphan drug designation (ODD), fast track designation (FTD), and rare pediatric disease designation. Additionally, under the European Medicines Agency and MHRA, the drug has also received ODD, FTD, and Advanced Therapy Medicinal Products. If a biologics license application for the treatment is submitted to the FDA, it will receive a priority review voucher.

References

1. OS Therapies granted U.S. FDA Type C Statistical Methods meeting to review 2.5-year overall survival data for OST-HER2 in the prevention or delay of recurrence in fully resected, pulmonary metastatic osteosarcoma. News release. OS Therapies. August 13, 2026. Accessed August 14, 2026. https://tinyurl.com/3vszsft7
2. OS Therapies achieves statistically significant 2.5-year overall survival in phase 2b trial of ost-her2 in fully resected pulmonary metastatic osteosarcoma. News release. OS Therapies. June 2, 2026. Accessed August 14, 2026. https://tinyurl.com/5ykcab3y
3. OS Therapies announces statistically significant positive interim 2-year overall survival data from phase 2b clinical trial of OST-HER2 in the prevention or delay of recurrent, fully resected, pulmonary metastatic osteosarcoma. News release. OS Therapies. August 7, 2025. Accessed August 14, 2026. https://tinyurl.com/2f8d62ct
4. OS Therapies presents statistically significantly positive 1-Year event free survival, overall survival and safety clinical data updates for OST-HER2 at the MIB Agents Factor Osteosarcoma Conference. News release. OS Therapies. June 30, 2025. Accessed August 14, 2026. https://tinyurl.com/ysmsw7pp
5. 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. OS Therapies. January 15, 2025. Accessed August 14, 2026. https://tinyurl.com/2tu9e5zb