Outcome of dogs with low- and high-grade mast cell tumors treated with electrochemotherapy

Abstract

BACKGROUND: Mast cell tumors (MCTs) in dogs pose therapeutic challenges that vary with histopathological grade. HYPOTHESIS/OBJECTIVES: Electrochemotherapy (ECT) alone would result in a clinically meaningful response in nonmetastatic cutaneous MCTs, with efficacy varying by tumor grade. ANIMALS: Twenty-nine client-owned dogs with 39 nonmetastatic cutaneous MCTs were treated at a veterinary oncology referral center. Tumors were classified as low grade (n = 27) or high grade (n = 12) according to the Kiupel system. METHODS: This retrospective cohort study evaluated outcomes after ECT as the sole treatment. The primary outcomes were complete remission (CR) rate, median survival time, and disease-free interval. Electrochemotherapy was administered using standardized protocols, with follow-up ranging from 30 to 1600 days. RESULTS: Overall complete remission rate was 79% (95% CI, 63.5-90.7). Complete remission was achieved in 100% of low-grade tumors (27/27; 95% CI, 87.2-100) versus 45% of high-grade tumors (5/12; 95% CI, 18.1-75.4). Median survival time was 1198 days (range 188-1920 days) for low-grade MCTs and 210 days (range 45-765 days) for high-grade MCTs (P = .001). Median disease-free interval was 1080 days (range 188-1920 days) and 455 days (range 45-865 days) for low- and high-grade tumors, respectively. Median tumor volume was 4.8 cm3; low-grade tumors were generally smaller. The average number of treatments was 1.1 for low-grade and 1.6 for high-grade tumors. CONCLUSIONS AND CLINICAL IMPORTANCE: ECT is an effective local treatment for low-grade MCTs, offering outcomes comparable to surgical management. For high-grade tumors, its benefit is limited to small-volume disease where surgery is not feasible.