A phase II clinical trial of vinorelbine in dogs with cutaneous mast cell tumors

Background: Few effective drugs are available to treat dogs with locally aggressive or metastatic mast cell disease. Hypothesis: Vinorelbine, a semisynthetic derivative of vinblastine, is an effective drug for the treatment of canine mast cell tumors (MCT). Animals: Twenty-four dogs with cutaneous MCT. Methods: Dogs with at least 1 measurable, cytologically confirmed, and previously untreated cutaneous MCT received a single treatment with vinorelbine at the previously established dosage of 15mg/m² IV. Tumor measurements and CBC were evaluated before and 7 days after treatment. Adverse events were graded according to Veterinary Cooperative Oncology Group (VCOG) guidelines. Statistics: Data were accrued in accordance with a Simon's 2-stage design with a noninteresting response rate of .05, a target response of .25, and α and β values of .10. Results: Three of 24 dogs (13%) had a response to treatment, including 1 measurable complete response and 1 measurable partial response. The 3rd dog had microscopic complete response to treatment with stable measurable disease. Twenty other dogs (83%) had stable disease and 1 dog (4%) had progressive disease. Neutropenia occurred in 13 dogs (54%) (grade 1, n = 4; grade 3, n = 6; grade 4, n = 3). Gastrointestinal toxicity occurred in 11 dogs (46%) (anorexia: grade 1, n = 3; grade 2, n = 1; grade 3, n = 1; diarrhea: grade 1, n = 2; grade 3, n = 1; vomiting: grade 1, n = 5; grade 3, n = 1). Conclusions and Clinical Importance: Vinorelbine was associated with an overall response rate of 13% and a high prevalence of neutropenia. Additional studies are indicated to determine if repeated dosing of vinorelbine or combination of vinorelbine with other drugs increases the observed biologic activity against canine MCT.