Multi-agent chemotherapy for mast cell tumours in the dog

Seventeen dogs with mast cell tumours received chemotherapy. Fifteen dogs were treated with a vincristine, cyclophosphamide, hydroxyurea, and prednisolone (VCHP) regimen. Seven of these were later switched to doxyrubicin and prednisolone either because they stopped responding or because they did not respond from the start of the treatment. Two dogs received the latter regimen as the primary therapy. All dogs were treated with cimitidine and metoclopramide to minimize the effect of paraneoplastic syndrome associated with histamine release. Ten of the 17 dogs were found to respond (4/17 complete response (CR), 6/17 partial response (PR)). Response duration varied from 39 to 910 days (median 53 days), including 3 dogs with a CR that lasted more than 2 years. Survival time in responders varied from 41 to 910 days (median 97 days) and from 30 to 126 (median 39) in the other 7 dogs. Dogs that became refractory to VCHP did not respond to doxyrubicin and prednisolone. It is concluded that multi-agent chemotherapy has anti-tumour activity in a considerable proportion of dogs with mast cell tumours, but its efficacy is variable. The multivariate analyses showed that significant factors predicting survival in dogs with mast cell tumours were sex (P = 0.009), absence or presence of non-abdominal distant metastases, or abdominal metastases, respectively (P = 0.023), and malignancy grade of the tumours (P = 0.053).