Treatment of canine mast cell tumors with CCNU (Lomustine)

The efficacy and toxicity of CCNU (1-[2-chloroethyl]3-cyclohexyl-1-nitrosur ea) were evaluated in 23 dogs with measurable mast cell tumors (MCT). Twent y-two dogs had cutaneous MCT and 1 dog had an intranasal MCT Nineteen (83%) dogs had biopsy of their original mass performed and 4 (17%) had aspiratio n cytology of masses. Of the 19 tumors histologically graded, 1 (5%) neopla sm was classified as grade I, 10 (53%) were grade II, and the remaining 8 ( 42%) were grade III. Dogs were treated with CCNU at a dosage of 90 mg/m(2) body surface area every 3 weeks. Response could be evaluated in 19 dogs. Ei ght of the 19 dogs (42%) had a measurable response to CCNU. One dog had a d urable complete response for 440 days. Seven dogs (37%) had a partial respo nse for a median and mean duration of 77 days and 109 days, respectively (r ange, 21-254 days). Treatment with CCNU resulted in stable disease in 6 dog s (32%) for a median and mean duration of 78 days and 122 days, respectivel y (range, 42-347 days). The acute dose-limiting toxicity was neutropenia 7 days after administration of CCNU. The median and mean neutrophil counts 7 days after CCNU were 1,452 cells/mu L and 1,683 cells/mu L, respectively (n = 17). Other toxicoses were uncommon. CCNU should be considered an active agent in the treatment of MCT in dogs.