Tolerability of a rapid‐escalation vinblastine‐prednisolone protocol in dogs with mast cell tumours

Optimal chemotherapy protocols for high‐risk mast cell tumours (MCTs) are unknown. The purpose of this study was to determine the tolerability and toxicity profile of a rapidly escalating vinblastine and prednisolone protocol (VPP) in which 3.00 mg/m(2) was administered once 7 days apart: at day 14 and at day 21. Dogs with chemotherapy‐naïve MCTs presenting to the Oncology Service of a single institution were prospectively enrolled to receive escalating vinblastine, and haematology and a standardised quality‐of‐life questionnaire were assessed prior to each dosage. Thirty‐four dogs were included: 30 with microscopic disease treated with adequate local therapy and four with macroscopic disease. Of 220 doses of vinblastine administered, 4% were associated with grade 3 and 4 toxicity. A total of 70% of dogs tolerated 3.00 mg/m(2) given 7 days apart at day 14 and 21, although 29% of dogs developed dose‐limiting toxicities and 8% discontinued the protocol due to toxicity. In conclusion, VPP was well‐tolerated overall, although prior to further dose intensity optimisation, it is important to determine if dose intensity is linked to outcome in canine MCT to avoid unwarranted toxicity.