Chlorambucil and prednisolone chemotherapy for dogs with inoperable mast cell tumours: 21 cases.

OBJECTIVES To evaluate the response of measurable canine mast cell tumours unsuitable for other treatment modalities to a chemotherapy protocol comprising chlorambucil and prednisolone. METHODS Dogs bearing measurable mast cell tumours, unsuitable for treatment by surgery or radiotherapy, were treated with orally administered prednisolone and chlorambucil, and their responses assessed. RESULTS Twenty-one dogs were enrolled in the study; 13 had intermediate-grade mast cell tumour, six were high grade and two were diagnosed by cytology alone. Eight dogs had multiple tumours and 13 dogs had single tumours, and six dogs had lymph node metastases and no dogs had visceral metastases detected. Three dogs achieved complete remission, five achieved partial remission (overall response rate 38 per cent), nine had static disease and four dogs had progressive disease. Median progression-free interval for the eight responders was 533 days, and median survival time for all dogs in the study was 140 days. Progression-free interval and median survival time were not influenced by the age, sex, weight or neutering status of the patient, by the grade or stage of the tumour or whether the patient had single or multiple tumours. No toxicity was detected. CLINICAL SIGNIFICANCE Response and survival rates of inoperable canine MCT to chlorambucil and prednisolone are comparable to previously described protocols, with no apparent toxicity.