OS Therapies' OST-HER2 (OST31-164), a HER2-targeted immunotherapy candidate, has shown statistically significant results in a Phase 2b clinical trial for patients with recurrent, fully resected osteosarcoma with lung metastases. The trial (NCT04974008) demonstrated a notable improvement in 12-month event-free survival (EFS) compared to historical controls, offering a potential new treatment option for this difficult-to-treat population. The company is now preparing to engage with the FDA for accelerated approval.
The Phase 2b study, an open-label, multicenter, single-arm trial, enrolled 39 evaluable patients aged 12 to 39 years with recurrent, fully resected lung-only metastatic osteosarcoma across 21 centers. Patients received OST-HER2 infusions every three weeks over 48 weeks and were followed for three years. The primary endpoint was EFS at 12 months, with secondary endpoints including overall survival (OS).
Significant Improvement in Event-Free Survival
The trial met its primary endpoint, demonstrating a 12-month EFS rate of 33.3% among patients treated with OST-HER2, compared to a peer-reviewed comparable historical control rate of 20% (P = .0158). This statistically significant improvement suggests a promising development for patients with this rare disease, for which there are currently no approved treatments.
Favorable Trend in Overall Survival
Interim analyses of the secondary endpoint, 3-year overall survival (OS), indicated a favorable trend for OST-HER2-treated patients at the 1-year and 2-year marks. At the 1-year interim timepoint, overall survival (OS) was 91% for OST-HER2 vs 80% for the historical control (P =.0700). At the 2-year interim timepoint, OS was 61% for OST-HER2 vs 40% for the historical control (P =.0576). Notably, all patients who achieved the primary 12-month EFS end point remain alive.
Safety Profile and Regulatory Strategy
The safety profile of OST-HER2 was deemed strong, with the treatment being well-tolerated during the study. This is particularly important in this patient population, which has limited treatment options. OS Therapies is preparing to engage with the FDA on an accelerated pathway for approval, leveraging the drug's rare pediatric disease designation.
Expert Commentary
"We are extremely pleased with these results of our phase 2b clinical trial because they show that OST-HER2-treated patients achieved the primary endpoint of 12-month EFS in a statistically significantly higher ratio than comparable historical controls, in addition to increasing the likelihood of 1-year and 2-year survival as compared with comparable historical controls," said Robert Petit, PhD, chief medical & scientific officer of OS Therapies. Paul Romness, MHP, chair & chief executive officer of OS Therapies, added, "The achievement of the primary endpoint in the OST-HER2 phase 2b is a tremendous success that opens the possibility, for the first time, of meaningful therapy for patients suffering from osteosarcoma with lung metastases after resection."
