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

  • J Vet Intern Med. 2026 May 4;40(3):aalag098. doi: 10.1093/jvimsj/aalag098.
Esther Chon  1 ,  Mohamad Morsey  1 ,  Terry Katz  1 ,  Kazumi Yamada  1 ,  Dennis Bailey  2 ,  Philip J Bergman  3  4 ,  Holly Burr  5 ,  Craig A Clifford  6 ,  Heather Heeb  7 ,  Christina Manley  8 ,  Brenda Phillips  9 ,  Gerald Post  10 ,  David M Vail  11  12 ,  Anthony Rusk  13 ,  Matthew L Stock  1
Affiliations
  • 1. Merck Animal Health, Rahway, NJ, United States.
  • 2. Oradell Animal Hospital, Paramus, NJ, United States.
  • 3. VCA Katonah Bedford Veterinary Center, Bedford Hills, NY, United States.
  • 4. VCA Clinical Studies, Los Angeles, CA, United States.
  • 5. Las Vegas Veterinary Specialty Center, Las Vegas, NV, United States.
  • 6. BluePearl Pet Hospital Malvern, Malvern, PA, United States.
  • 7. BluePearl Veterinary Specialty Hospital in Overland Park, Overland Park, KS, United States.
  • 8. The Oncology Service at the LifeCentre, Leesburg, VA, United States.
  • 9. Veterinary Specialty Hospital - Sorrento Valley, San Diego, CA, United States.
  • 10. MedVet Norwalk, Norwalk, CT, United States.
  • 11. Department of Medical Sciences, School of Veterinary Medicine, Madison, WI, United States.
  • 12. Carbone Comprehensive Cancer Center, University of Wisconsin-Madison, Madison, WI, United States.
  • 13. ACI Biosciences, LLC, Chevy Chase, MD, United States.
PMID: 42247661 DOI: 10.1093/jvimsj/aalag098
Abstract

Background: Immune checkpoint inhibitors (ICIs) have transformed oncology in human medicine, providing clinical benefit in a broad spectrum of cancers. Widely available ICIs for dogs are lacking.

Hypothesis/objectives: Evaluate efficacy and safety of gilvetmab, a caninized anti-PD-1 monoclonal antibody.

Animals: Fifty-one client-owned dogs were evaluated, 25 with stages II-III melanoma and 26 with stages I-III mast cell tumor (MCT). Fifteen dogs with stages III-V lymphoma were also evaluated.

Methods: Multi-institutional, open-label study. Enrolled dogs were treated with gilvetmab IV at 6 mg/kg q28d or 10 mg/kg q14d; 8 dogs receiving the lower dosage underwent dose escalation with their owners' consent. Safety was evaluated by physical examinations, laboratory testing, and clinical observations made by veterinarians or the dogs' owners. Efficacy was assessed by objective response rate (ORR) and time to progression (TTP) using cRECIST v1.0 and lymphoma response criteria.

Results: For melanoma, the ORR was 20% (95% confidence interval [CI], 7%-41%) and median TTP was 56 days. For MCT, the ORR was 46% (95% CI, 27%-67%) and median TTP was not reached. No objective responses were observed in dogs with lymphoma. Serious adverse events of anaphylaxis, hypotension, or tumor hemorrhage occurred in 3 dogs (3/51, 5.9%). Tumor enlargement before regression, consistent with possible pseudoprogression, was observed in 2 dogs with melanoma.

Conclusions and clinical importance: Gilvetmab has a reasonable expectation of efficacy and an acceptable preliminary safety profile in dogs with MCT stages I-III and melanoma stages II and III.

Keywords
PD-1; Programmed cell death 1 receptor; cancer; canine; immune checkpoint inhibitor; immunotherapy; monoclonal antibody.
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