Mast cell tumours in dogs — the cancer with the widest variability
Mast cell tumours are the canine cancer with the widest range of outcomes. The same diagnosis can mean a curative surgery on a Tuesday afternoon or a metastatic disease that ends a dog's life within months. Histopathology — specifically the grade — is the single most important variable. Below: how MCT presents, what the grading systems actually mean, and the decision points.
The Quality-of-Life Decision Pack
For when MCT is the high-grade kind.
The short answer
Mast cell tumours are common, variable in behaviour, and best treated by surgical excision with appropriate margins followed by histopathology. The histopathology grade is what tells you whether further treatment is needed. Without the grade, you do not have enough information to plan.
What it is
A cancer of mast cells — immune cells whose normal function is to release histamine and other inflammatory mediators. Tumours can occur anywhere there are mast cells, but most commonly arise as cutaneous (skin) lumps. Some are pink and hairless; others ulcerate; some look harmless and turn out to be aggressive on histopathology.
The "mast cell" name does not predict behaviour. The same diagnosis can describe a benign-looking pink dome that resolves with simple excision and an aggressive multi-systemic disease that ends a dog's life within months.
Breeds at risk
Boxers, Bulldogs, Boston Terriers, Pugs, Labradors, Golden Retrievers, Pit Bulls, and Shar Peis carry elevated risk. Boxers in particular often develop multiple low-grade MCT across their lifetime; the same Boxer who has had three excised by age 8 may live to 12 with no metastatic disease.
Grading — the deciding factor
Two grading systems, both pathology-based:
- Patnaik (1984) — three-tier (Grade I, II, III). Grade I is well-differentiated, low-risk; Grade III is poorly-differentiated, high-risk. Grade II is the problematic middle category — about 50% behave like I, the other 50% like III.
- Kiupel (2011) — two-tier (low-grade vs high-grade). Designed to address the Grade II ambiguity. Low-grade has >90% 2-year survival; high-grade has <25%.
Most modern reports include both grading systems plus c-kit mutation status (which guides response to tyrosine-kinase-inhibitor chemotherapy).
Surgery and margins
Surgical excision is the cornerstone of treatment. Recommended margins are 2–3 cm laterally and one fascial plane deep — significantly more aggressive than for a benign lump. Achieving these margins on a limb or near a face is sometimes impossible and reconstructive surgery is needed.
Margin status, reported on histopathology, dictates next steps:
- Complete margins: No further treatment for low-grade; chemotherapy considered for high-grade.
- Narrow / close margins: Re-excision or local radiation.
- Incomplete margins: Re-excision, radiation, or systemic therapy depending on grade.
Systemic treatment for high-grade or metastatic MCT
- Vinblastine + prednisolone: The classic protocol. Modest efficacy for high-grade.
- Tyrosine-kinase inhibitors (toceranib / Palladia, masitinib): Particularly effective in c-kit-mutant tumours. Oral, well-tolerated by most dogs.
- Lomustine (CCNU): An older agent still used for refractory cases.
Survival numbers
- Low-grade, completely excised: >90% 2-year survival; many cured.
- Low-grade, incompletely excised: Re-excision or radiation usually achieves similar outcome to complete excision.
- High-grade, with treatment: Median survival 6–12 months; long-term survival uncommon.
- Metastatic disease: Median 4–6 months on best available therapy.
Common questions
My vet says it is a mast cell tumour but did not grade it. Should I push?
Is a mast cell tumour curable?
Why does my dog look like he has hives around the tumour?
My dog has multiple mast cell tumours. Is that worse?
Editorial reference, not veterinary advice. — Dr. NRS, last reviewed 28 April 2026.