Phase 2b Trial of OST-HER2 Meets Main Goal in Preventing Recurrent Lung Metastatic Osteosarcoma

OS Therapies, Inc. has announced promising outcomes from its Phase 2b clinical trial of OST-HER2, an immunotherapy candidate for treating osteosarcoma with lung metastases. This trial focuses on preventing the recurrence of this rare form of cancer in pediatric patients who have undergone complete surgical removal of the lung metastases.

The trial results reveal that patients treated with OST-HER2 had a significantly higher rate of 12-month event-free survival (EFS) compared to historical controls. Defined as the period without disease recurrence, the 12-month EFS was 33% for OST-HER2 recipients, compared to 20% for those in the control group. This marks a notable achievement in the study's primary objective. Additionally, interim analyses suggest a favorable trend for overall survival (OS) at one and two years for patients receiving OST-HER2, with survival rates of 91% and 61%, respectively, compared to 80% and 40% for the historical control group.

Dr. Robert Petit of OS Therapies expressed satisfaction with these results, highlighting the statistically significant improvement in the primary endpoint and the encouraging trend in OS. He also emphasized the strong safety profile of OST-HER2, which reinforces its potential as a treatment option for a challenging patient population with no approved therapies currently available.

Paul Romness, CEO of OS Therapies, hailed the trial's success as a significant breakthrough, potentially offering a meaningful treatment for patients with resected lung metastatic osteosarcoma. He noted that the company's regulatory strategy aligns with the FDA's recent guidelines for accelerated approvals. This paves the way for discussions with the FDA regarding expedited approval processes, with plans to proceed without the need for additional patient treatments.

The trial enrolled 39 patients aged 12 to 39, all with recurrent, fully resected lung-only metastatic osteosarcoma. Conducted across 21 centers, the trial involved a single treatment arm, with patients receiving 16 doses over 48 weeks. Follow-up visits were scheduled four weeks after the last dose. The promising outcomes indicate a potential new therapy for an otherwise difficult-to-treat condition.

In post-hoc analyses, the study examined various subgroups. It found that females in the OST-HER2 group had a 47% rate of 12-month EFS, compared to 20% for males. Also, patients with two or more prior lung resections showed a 55% rate of 12-month EFS, versus 25% for those with only one prior resection.

OST-HER2 employs a form of Listeria bacteria engineered to target cancer cells expressing the HER2 protein. The therapy aims to prevent metastasis, delay recurrence, and eradicate primary tumors, potentially working alongside approved therapies to improve survival outcomes. OST-HER2 has garnered several designations from regulatory bodies, including Rare Pediatric Disease Designation and Fast Track Status from the FDA, and Orphan Drug Designation from both the FDA and the EMA.

OS Therapies is exploring the potential market value of OST-HER2, particularly in preventing lung metastases, which is estimated at over $500 million. With the rare pediatric disease priority review voucher (PRV) program, the company anticipates leveraging its awarded PRV to further its efforts in developing therapies for rare pediatric conditions like osteosarcoma. Despite recent legislative challenges regarding the PRV program, OS Therapies remains poised to benefit from this opportunity, given its existing designations and anticipated timelines for approval.