Serious severity
Mast Cell Tumour
A tumour arising from mast cells, the immune cells that store histamine. In cats it usually appears as a small firm skin lump, but it can also affect the spleen and intestine.
⚠️ Common symptoms
Mast cells are the immune system's alarm cells. They sit in the skin, gut and airways packed with granules of histamine and other inflammatory chemicals, ready to dump their contents at the first sign of injury or allergen. A mast cell tumour is a growth of these cells, and it carries an unusual dual threat: the physical presence of the mass, and the biochemical havoc that occurs when a large population of unstable mast cells releases histamine into the body.
In cats the disease takes three broadly distinct forms. The cutaneous form is the most common and the most benign in behaviour — typically a solitary, firm, hairless, dome-shaped lump a centimetre or less across, often on the head or neck, and frequently in an older cat. Complete surgical removal is usually curative, and cats do not follow the aggressive grading-driven pattern that makes canine mast cell tumours so feared.
The splenic form is distinctive to cats and accounts for a substantial share of all feline splenic disease. Affected cats present vaguely — losing weight, vomiting intermittently, not quite right — and an enlarged spleen is found on examination or ultrasound. What surprises many owners is how well these cats do after splenectomy. Even when mast cells are already circulating in the blood or present in the liver, median survival after removal of the spleen is often measured in years rather than months.
The intestinal form is the least common and by far the most serious, tending to present late with vomiting, diarrhoea and weight loss, and to have spread by the time it is found.
Across all forms, histamine is the complication to watch. Excess circulating histamine drives acid secretion in the stomach, and gastric ulceration is common enough that most oncologists put affected cats on an acid blocker as a matter of routine. Manipulating a tumour — even just squeezing it during an examination — can cause a sudden release of granule contents and local swelling and redness, a phenomenon known as Darier's sign.
For young Siamese cats with multiple skin nodules, it is worth knowing that a well-described histiocytic variant exists which can regress entirely on its own over several months. It is one of the few cancers in veterinary medicine where "wait and monitor" is a legitimate plan, though the diagnosis must be confirmed first.
🔍 Causes
The underlying cause of feline mast cell neoplasia is not known. Mutations in the KIT receptor gene, which drives mast cell growth and survival, are found in a proportion of cases and can make the tumour susceptible to targeted drugs called tyrosine kinase inhibitors. Siamese cats are over-represented, particularly for a distinctive histiocytic form that appears in young cats as multiple skin nodules and which sometimes regresses spontaneously without any treatment at all. No dietary, environmental or infectious trigger has been established.
🛡 Prevention
There is no known way to prevent mast cell tumours. The practical equivalent of prevention is early detection: run your hands over your cat once a month, feeling systematically over the head, neck, body and limbs, and have any new lump measured and examined. A fine-needle aspirate is quick, usually needs no sedation, and mast cells have such distinctive purple granules that the diagnosis is often made from that single test.
💊 Treatment
Skin mast cell tumours in cats are usually treated by surgical removal, and the outlook after complete excision is good — considerably better than for the equivalent tumour in dogs. Splenic mast cell disease is treated by removing the spleen, which sounds drastic but is remarkably well tolerated and often gives long survival times even when the disease has spread to other organs. Intestinal mast cell tumours are the most aggressive form and carry the poorest prognosis. Supportive medication almost always includes antihistamines and a stomach protectant such as omeprazole, because histamine released by the tumour cells causes gastric ulceration.
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⚕️ Medical disclaimer
- This information is educational only and is not a substitute for veterinary advice.
- Symptoms overlap between conditions — only a vet can diagnose accurately.
- Never withhold treatment or self-medicate based on information found online.
- When in doubt, call your vet. Early intervention almost always leads to better outcomes.