OS Therapies has filed a new patent application covering a novel immune-response biomarker associated with its lead cancer immunotherapy candidate, OST-HER2. The filing is based on recent data from a Phase IIb clinical trial targeting recurrent, fully resected pulmonary metastatic osteosarcoma.

The company said the identified biomarker signature reflects a dual immune response—downregulation of genes linked to tumour immune evasion and upregulation of genes responsible for cytotoxic immune activation—resulting in enhanced anti-tumour activity. This “turning cold tumours hot” mechanism is considered a significant advancement in immunotherapy approaches.

According to the company, the biomarker meets criteria outlined under the U.S. Food and Drug Administration Biomarkers, EndpointS and other Tools (BEST) programme, potentially qualifying it as a surrogate endpoint for evaluating treatment outcomes such as one-year event-free survival and two-year overall survival.

The findings are expected to play a key role in upcoming regulatory engagements with global agencies, including the European Medicines Agency, the Medicines and Healthcare products Regulatory Agency, and the Therapeutic Goods Administration. The company plans to submit its first regulatory filing for OST-HER2 to the European regulator by the end of April 2026.

OST-HER2 is a Listeria-based immunotherapy designed to stimulate targeted immune responses against HER2-expressing cancer cells. The therapy has already received multiple regulatory designations, including Orphan Drug and Fast Track status, reflecting its potential in addressing high unmet medical needs.

OS Therapies aims to seek accelerated approval for the therapy in 2026, while also exploring its application in other cancers such as breast and bladder cancer.