Efficacy and safety evaluation of gilvetmab in dogs with melanoma and mast cell tumor.

Gilvetmab shows promising efficacy in canine mast cell tumors (46% ORR) with an acceptable safety profile.

This multi-institutional, open-label study evaluated the efficacy and safety of gilvetmab, a caninized anti-PD-1 monoclonal antibody immune checkpoint inhibitor (ICI), in 51 client-owned dogs with melanoma (n=25, stages II-III) or mast cell tumor (MCT; n=26, stages I-III), with an additional 15 dogs with lymphoma (stages III-V). Dogs received gilvetmab IV at 6 mg/kg q28d or 10 mg/kg q14d, with 8 dogs undergoing dose escalation. Efficacy was assessed using cRECIST v1.0 criteria and lymphoma response criteria. For melanoma, the objective response rate (ORR) was 20% (95% CI: 7%-41%) with a median time to progression (TTP) of 56 days. MCT demonstrated a more promising ORR of 46% (95% CI: 27%-67%) with median TTP not reached, suggesting durable responses in a subset of patients. No objective responses were observed in lymphoma patients. Serious adverse events, including anaphylaxis, hypotension, and tumor hemorrhage, occurred in 5.9% of dogs (3/51). Notably, two melanoma patients exhibited tumor enlargement prior to regression, consistent with pseudoprogression, a phenomenon also observed with ICIs in human oncology. Overall, gilvetmab demonstrated an acceptable preliminary safety profile and reasonable efficacy, particularly in MCT. These findings support further investigation of gilvetmab as a viable immunotherapeutic option for canine MCT and melanoma, while highlighting the need for larger controlled trials to better define optimal dosing, patient selection, and long-term outcomes.

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