Predicting dog tumor response to vincristine

Abstract

BACKGROUND: Vincristine is the standard treatment for canine transmissible venereal tumor (CTVT), and its combination with ivermectin has yielded inconsistent results. These discrepancies may reflect differences in tumor aggressiveness. HYPOTHESIS/OBJECTIVES: We hypothesized that ivermectin's efficacy depends on tumor aggressiveness and would be more beneficial in aggressive CTVTs. Our objective was to evaluate the treatment response and physiologic impact of combination versus monotherapy across tumor aggressiveness categories. ANIMALS: Twenty client-owned dogs with cytologically-confirmed CTVT were enrolled. Tumors were classified as aggressive or non-aggressive based on a structured scoring system. METHODS: Randomized, placebo-controlled, double-blinded clinical trial. Dogs received vincristine monotherapy (0.5 mg/m2 IV weekly) or vincristine plus ivermectin (0.5 mg/kg SC × 2). The primary outcome was treatment duration (weeks to confirmed remission). Hematologic and biochemical tests were monitored weekly. Data were analyzed by analysis of variance and Tukey honestly significant difference. RESULTS: Treatment duration was significantly decreased in the combination treatment group, especially for aggressive tumors (aggressive: 4.3 ± 0.3 vs. 5.9 ± 0.2 weeks, P = .003; non-aggressive: 3.8 ± 0.2 vs. 5.5 ± 0.3 weeks, P = .0004). No significant differences in red or white blood cell parameters were observed. CONCLUSIONS AND CLINICAL IMPORTANCE: Ivermectin significantly shortened treatment duration when added to vincristine, particularly in aggressive CTVT, without inducing hematology or renal toxicity. These findings emphasize the importance of tumor stratification in evaluating adjunctive treatments.