Clinical response of masitinib mesylate in the treatment of canine macroscopic mast cell tumours

OBJECTIVES: To retrospectively evaluate the clinical response and toxicity associated with masitinib mesylate (Masivet®) treatment of macroscopic mast cell tumours in the dog. METHODS: Retrospective review of medical records of 39 dogs that had undergone treatment with masitinib for macroscopic mast cell tumours. Patient signalment, tumour location, tumour grade, tumour stage, previous treatments, concurrent medications, dose of masitinib, side effects, response, time to tumour progression, survival time and cause of death were documented. Response was assessed according to RECIST criteria. RESULTS: Clinical response was observed in 32 (82·1%) dogs receiving masitinib, with 15 dogs (38·5%) exhibiting a complete response and 17 dogs (43·6%) achieving a partial response. The median time to progression was 79 days (range: 14 to 667 days). Adverse effects were seen in 25 dogs (64·1%) with serum alanine aminotransferase elevation (n=9; 23·1%) and vomiting (n=6; 15·4%) being most common. Median survival time following initiation of masitinib was 159 days (range: 14 to 1339). CLINICAL SIGNIFICANCE: Masitinib appears to be a well-tolerated and effective drug against macroscopic mast cell tumours.