Rockville, Maryland, June 26, 2026
OS Animal Health announced the peer-reviewed publication of Phase 2 clinical trial results evaluating OST-HER2 combined with palliative radiation therapy (RT) as a frontline treatment for canine osteosarcoma. The study demonstrated a median overall survival of 159 days for dogs treated with OST-HER2 plus radiation, compared with 124 days for radiation therapy alone (p=0.0237). Long-term survival also improved significantly, with 20% of treated dogs surviving two years versus 1% in the control group (p=0.00995). The company plans to request a meeting with the U.S. Department of Agriculture (USDA) during the third quarter of 2026 to discuss the regulatory pathway toward conditional approval of OST-HER2 for canine osteosarcoma.
Phase 2 Study Shows Significant Survival Benefit
The Phase 2 trial evaluated OST-HER2 immunotherapy alongside palliative radiation therapy in dogs with frontline canine osteosarcoma, aiming to provide an alternative for patients where amputation is not preferred. Results showed 33% one-year survival, 27% survival at 500 days, and 20% survival at two years among treated dogs, compared with 13%, 2%, and 1%, respectively, in the radiation-only group. Researchers believe the findings provide the first clinical evidence that combining OST-HER2 with radiation may allow a subset of dogs to avoid amputation, maintain limb function, delay metastatic progression, and achieve improved quality of life. The study also reinforces the potential of HER2-targeted immunotherapy as a new treatment strategy for veterinary oncology.
Regulatory Plans and Commercial Expansion
With more than 15,000 dogs diagnosed annually with osteosarcoma in the United States, OS Animal Health is preparing for regulatory discussions with the USDA to advance OST-HER2 toward market. The company also announced plans to launch a crowdfunding campaign during the third quarter of 2026 to expand its shareholder base ahead of a proposed public listing. In parallel, parent company OS Therapies reiterated its intention to distribute OS Animal Health shares to existing shareholders following the subsidiary’s planned public market transaction. The company believes the growing adoption of molecularly targeted therapies in animal health creates an opportunity for OST-HER2 to become a platform treatment for HER2-positive canine cancers beyond osteosarcoma.
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Comparative Oncology Supports Human Development
OST-HER2 is an off-the-shelf Listeria-based cancer immunotherapy designed to stimulate immune responses against HER2-positive tumors. The therapy has already received conditional USDA approval for canine osteosarcoma and is being advanced toward renewed regulatory authorization. The company also highlighted the importance of comparative oncology, noting that canine osteosarcoma closely resembles the human disease in genetics, immune response, and disease progression. Positive findings from veterinary studies could therefore support future human clinical development, where OST-HER2 has already demonstrated encouraging Phase 2b results in recurrent lung metastatic osteosarcoma and is expected to support a Biologics License Application (BLA) submission to the U.S. FDA in 2026.
Source: OS Therapies press release
