Mast cell tumors are the most common malignant skin tumor in dogs, with a wide spectrum of behavior from indolent to aggressive, requiring careful welfare-focused treatment decision-making.
MCTs that degranulate — releasing histamine — cause local pain, swelling, and systemic gastrointestinal signs including nausea and ulcers. Surgical excision requires appropriate margins, sometimes meaning significant tissue removal. High-grade MCTs treated aggressively with chemotherapy subject dogs to treatment side effects — vomiting, diarrhea, neutropenia — that must be weighed against benefit. For dogs with advanced MCTs, the welfare question of treatment versus palliation requires honest assessment of likely outcomes versus treatment burden. Palliative management with prednisolone and diphenhydramine can control symptoms and maintain quality of life in dogs for whom curative intent is not appropriate. The emotional burden on owners navigating cancer diagnosis and treatment decisions adds complexity to the welfare picture.