When is electrochemotherapy indicated for mast cell tumors and what are the reported response rates?

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Electrochemotherapy (ECT) is indicated for canine and feline mast cell tumors (MCTs) when surgical excision is not feasible due to anatomic location, when margins are incomplete, or as an alternative to surgery for smaller lesions. Common anatomic indications include the head, periocular region, and hindlimb — sites where curative surgery would involve cosmetic or functional compromise. 8 In dogs, ECT alone achieves complete response rates of 62–77%, with the highest local tumor control reported when ECT is combined with interleukin-12 (IL-12) gene electrotransfer (GET). ECT combined with peritumoral IL-12 GET achieves a complete response rate of 72% in canine MCTs. 12 When IL-12 GET is delivered intratumorally rather than peritumorally, local tumor control, disease-free interval, and progression-free survival are all significantly better, making intratumoral IL-12 GET the preferred route when this combination is used. 6 ECT alone, ECT + peritumoral IL-12 GET, and ECT + intratumoral IL-12 GET represent three distinct tiers of efficacy, with the intratumoral combination performing best across all outcome measures. 6 In cats, ECT with intravenous bleomycin at 15,000 IU/m² achieves complete resolution in all treated patients across a range of presentations, including multiple MCTs (7–50 nodules, 0.2–1 cm) and solitary large tumors up to 4.6 cm. 3 No tumor recurrence was detected over follow-up periods ranging from 210 to 810 days, though one patient developed new lesions at day 210. 3 One to two ECT sessions were required, with 14–45 days between sessions. 3 ECT is specifically recommended over tigilanol tiglate or electrochemotherapy in the periocular and mucosal regions of the head, where tigilanol tiglate and ECT are associated with pain, necrosis, open wounds, and scabbing lasting weeks — adverse effects that are particularly problematic near the conjunctiva. 2 Local toxicity from ECT in canine MCT cases is graded 1–4 on a 5-point scale (0 = no toxicity, 5 = highes