Masitinib mesylate for metastatic and non‐resectable canine cutaneous mast cell tumours

Masitinib mesylate is a tyrosine kinase inhibitor approved for the treatment of gross, non-metastatic grade II and III canine mast cell tumours (MCTs). This study evaluated the use of masitinib as a frontline and rescue agent for metastatic and non-metastatic canine MCTs. Identification of toxicities and prognostic factors in these dogs was of secondary interest. Twenty-six dogs were included in this study. The overall response rate to masitinib was 50%. The median survival time for dogs that responded to masitinib was 630 days versus 137 days for dogs that did not respond (P = 0.0033). Toxicity was recorded in 61.5% of treated dogs, but the majority of adverse events were mild and self-limiting. Response to masitinib, not tumour grade, stage or location, was the most significant prognostic factor for survival in dogs with MCTs.