What are Mast Cell Tumours in Dogs
Mast cells are normal cells found in most organs and tissues of the body and are present in the highest numbers in locations that interface with the outside world, such as the skin, the lungs and the stomach and bowels. They contain granules of a chemical called histamine, which is important in the normal response of inflammation.
When mast cells become cancerous, mast cell tumours (MCTs) are formed. Mast cell tumours range from being relatively benign and readily cured by surgery, through to showing aggressive and much more serious spread through the body.
The cause of this transformation is unknown, but some breeds of dog are predisposed to the condition, and this probably suggests an underlying genetic component.
Written by Dr. Mariella Roberts, Veterinary Surgeon, Animal Trust Vets CIC | Published November 2025 | Review date November 2028| This advice is for UK pets only and is not a replacement for seeing a vet
Symptoms of Mast Cell Tumours
MCTs commonly present as lumps or bumps on or just below the skin's surface
they can be raised, flat, or even ulcerated, and their size can vary greatly
the skin around the tumour may be red and inflamed, and the mass itself may swell or increase in size rapidly
some MCTs are itchy, causing dogs to lick or scratch the area
MCTs can grow and shrink quickly, or they might appear suddenly and then persist
If the tumour spreads or releases chemicals, then general symptoms maybe encounter such as:
no eating
vomiting or diarrhoea
weight loss
When to contact your vet
if you notice any new lumps or changes in existing lumps
lumps that are very itchy, red or inflamed
lumps that grow quickly
Diagnosing MCTs
history and clinical exam
FNA (fine needle aspirate) thin needle is inserted into the mass to collect cells, which are then smeared on a slide and examined under a microscope (cytology)
biopsy (surgical removal of a tissue sample) may be recommended to determine the tumor's grade and aggressiveness
grading and staging to determine how likely they are to spread
additional test maybe requires such as blood test and X-rays for overall check and extent of the tumour
Treatment of Mast Cell Tumours in Dogs
Surgical removal with wide margins is the cornerstone of treatment for most MCTs. The goal is to remove the entire tumour and surrounding tissue to ensure clean margins (absence of cancerous cells).
Chemotherapy may be used before surgery to shrink the tumour, after surgery to target any remaining cancer cells, or as a palliative treatment when complete surgical removal is not possible.
Radiation can be used to target microscopic cancer cells, especially after surgery, or as a palliative treatment for non-operable tumours.
Prevention
Unfortunately, there's no known way to definitively prevent mast cell tumors (MCTs) in dogs.
Early detection through regular skin checks and prompt veterinary attention for any suspicious lumps is crucial for successful treatment.
Outlook
The outlook for dogs with mast cell tumours (MCTs) varies significantly depending on several factors, primarily tumour grade and stage. Low-grade MCTs, when completely removed with clean surgical edges, often have a good outcome and can be cured. However, high-grade MCTs, or those that have already spread (metastasised), generally have a poorer outlook, even with treatment.