Mast cell tumours are the most common malignant skin tumours in dogs, with behaviour ranging from benign to aggressive, requiring grading, staging, and treatment decisions that significantly affect welfare outcomes.
Mast cell tumour welfare implications depend heavily on grade and stage. Dogs with low-grade MCTs treated by adequate surgical excision typically experience minimal lasting welfare harm — surgery is a single intervention with a good cure rate. High-grade MCTs carry poor prognoses and may require aggressive multimodal treatment with significant side effects, or palliative management focused on comfort. The degranulation phenomenon is an important welfare consideration: manipulation of MCTs (including incomplete excision or aggressive handling) triggers release of vasoactive substances causing local swelling, systemic hypotension, and gastrointestinal ulceration. Antihistamine pre-treatment before surgery and diphenhydramine administration reduce degranulation complications. For dogs with advanced disease, quality of life assessment guides the choice between aggressive treatment and palliative care.