Merck Animal Health Highlights Landmark Clinical Research on Gilvetmab, the First Caninized Immune Checkpoint Inhibitor for Canine Oncology in the Journal of Veterinary[...]

Data published in leading veterinary journals demonstrate significant clinical benefit and durable tumor response in dogs with melanoma or mast cell tumor

RAHWAY, N.J., October 1, 2026 - Merck Animal Health, a division of Merck & Co., Inc., Rahway, N.J., USA (NYSE:MRK), today announced the publication of two peer-reviewed studies evaluating the safety and efficacy of gilvetmab, a first-in-class caninized anti-programmed cell death protein 1 (anti-PD-1) monoclonal antibody, in dogs with spontaneous malignancies.

A study published in the Journal of Veterinary Internal Medicine titled "Efficacy and safety evaluation of gilvetmab in dogs with melanoma and mast cell tumor," provides clinical evidence assessing the caninized immune checkpoint inhibitor's objective response rates, disease control, safety parameters, and immunological dynamics across canine oral and cutaneous melanoma and mast cell tumor (MCT). A study published in the Journal of the American Veterinary Medical Association titled "Gilvetmab advances immune checkpoint inhibitor immunotherapy for canine cancer" describes how immune checkpoint inhibitors (ICIs) are emerging as a promising strategy in veterinary oncology by unleashing antitumor immunity to target canine cancers.

"At Merck Animal Health, we are committed to advancing breakthrough innovations that address significant unmet medical needs in veterinary medicine," said Christine Royal, DVM, vice president, companion animal and equine business unit, Merck Animal Health. "Canine oncology has historically faced a substantial shortage of targeted immunotherapies. By investing in foundational biotherapeutic platforms and rigorous, peer-reviewed clinical trials, we remain dedicated to advancing veterinary science and empowering veterinary oncologists with evidence-based therapeutic options for complex, life-limiting conditions. Importantly, by generating robust clinical data, we can help veterinarians make more informed treatment decisions and ultimately improve outcomes for animals and the people who care for them."

Gilvetmab is an immune checkpoint inhibitor designed specifically for dogs. The product containing gilvetmab, a caninized monoclonal antibody against canine programmed cell death receptor-1 (PD-1), is conditionally approved by the USDA for the treatment of dogs with melanoma or mast cell tumor. It binds canine PD-1 to disrupt inhibitory signaling between PD-1 and its ligands (PD-L1 and PD-L2), thereby counteracting tumor-mediated T-cell suppression and reactivating anti-tumor immune responses.

This product has demonstrated a reasonable expectation of efficacy and a preliminary safety profile in reducing the solid tumor burden in dogs with stage II and III melanoma and dogs with stage I, II, and III mast cell tumor. Because this product license is conditional, safety, efficacy, and potency have not been fully evaluated. Gilvetmab is currently only available in the United States, and additional studies are in progress to further support its safety and efficacy. Production under this license is in compliance with all regulations and standards applicable to such products. For more information regarding safety, see productdata.aphis.usda.gov.

The peer-reviewed clinical findings evaluate gilvetmab as an innovative immunotherapy that unleashes the dog's own immune system to fight difficult-to-treat canine cancers. The research evaluated canine patients diagnosed with oral malignant melanoma and cutaneous or subcutaneous mast cell tumor (MCT), two aggressive and common cancers in companion animal oncology.

Key Findings:

-Substantial Clinical Benefit: Gilvetmab delivered an overall clinical benefit rate (defined as complete response, partial response, or stable disease) of 66.7% across evaluated canine patients with melanoma or mast cell tumor.
-Meaningful Activity in Advanced Melanoma: Dogs with Stages II-III oral malignant melanoma achieved an Objective Response Rate (ORR, defined as complete response or partial response) of 20%, and 40% of dogs maintained stable disease, offering a vital alternative for dogs with limited treatment options.
-Durable Responses in Mast Cell Tumors: Dogs with Stages I-III mast cell tumors achieved an ORR of 46%, with a median Time to Progression (TTP) that was not reached during the evaluation window, demonstrating long-lasting disease control.
-Favorable Safety and Quality of Life: Gilvetmab was well-tolerated as a 30-minute IV infusion following premedication with diphenhydramine, with 96% of canine patients maintaining a high quality of life throughout therapy. Serious adverse events were uncommon (5.9%) and manageable with standard clinical intervention.

"This clinical trial of gilvetmab represents an important milestone in translational immuno-oncology, establishing baseline pharmacokinetic, safety, and response benchmarks for checkpoint inhibition in veterinary medicine," said Laura Greene DVM, DACVIM, internal medicine specialist, Merck Animal Health. "While checkpoint blockade has become a cornerstone of treatment across many human cancers, the availability of immune checkpoint inhibition in veterinary medicine represents a new frontier in canine cancer care. These findings provide important evidence supporting the use of PD-1 pathway inhibition in dogs with cancers such as melanoma and mast cell tumor, and help define the role of this emerging therapeutic class."

ICIs focusing primarily on the biologically conserved PD-1/PD-L1 pathway help reverse tumor-induced immune exhaustion, showing favorable safety and notable clinical activity in treating spontaneously occurring canine melanoma and mast cell tumor. While these therapies offer a major step forward, ongoing research remains vital to optimizing patient selection, identifying robust biomarkers, managing immune-mediated side effects, and developing effective combination protocols to fully realize the potential of immunotherapy for companion animals.

About Merck Animal Health

Merck Animal Health, a division of Merck & Co., Inc., Rahway, N.J., USA, is a global animal health business committed to The Science of Healthier Animals™. For more than 130 years, we have pioneered groundbreaking science. Today, we are driven by continuous innovation to develop breakthrough medicines, vaccines and technology. Rooted in direct experience on the farm and in the clinic, we work hand in hand with our customers every step of the way. Our singular focus is to empower those who care for animals, helping them manage their vital responsibility with confidence. Because when it comes to animal health, no one sees it like we do. For more information, visit www.merck-animal-health.com and connect with us on LinkedIn, Facebook, X (formerly Twitter) and Instagram.

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