The statement about recurrence needs qualification: many solitary skin mast cell tumours respond well to surgery. Not all therefore readily recur or spread. Location, tissue sample characteristics and disease extent matter more than the name alone.
When to see a vet urgently
Seek emergency care if your cat has any of the following:
- Vomiting blood or black, tarry stools.
- Sudden severe weakness, pale mucous membranes or collapse.
- Difficulty breathing or rapidly deteriorating general health.
- Heavy or continuous bleeding from the tumour area.
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Overview
Mast cells contain granules holding biologically active substances, including histamine and heparin. When these cells multiply uncontrollably, skin lumps develop and may ulcerate and become inflamed. Feline skin mast cell tumours are usually fairly benign, whereas internal forms affecting the spleen and intestines are aggressive.
The internal forms also differ from one another. A splenic mast cell tumour may benefit considerably from spleen removal, and does not automatically have the same prognosis as an intestinal tumour. Intestinal forms are often harder to treat, but their prognosis also varies. Location and extent are established before treatment decisions.
A cat can have an internal mast cell tumour without skin lumps. Conversely, skin lesions and internal disease can occur in the same animal. Examining the skin alone therefore does not establish the full disease extent.
Causes
The exact causes of mast cell tumours are unknown, but several factors are associated with them:
- Hereditary predisposition, with Siamese cats more often affected.
- Chronic skin inflammation.
- Age-related changes, with older cats more often affected.
- Immune system disorders.
The precise trigger is usually unknown. Susceptibility observed in Siamese cats does not mean a hereditary disease has been demonstrated behind every tumour. Nor can the role of chronic skin inflammation or immune dysfunction be inferred from one lump. A tumour is not the same as an ordinary allergic skin reaction.
Risk factors
- Older cats, over 8 years old.
- Siamese and Oriental cats.
- Cats with chronic skin inflammation or nodular skin lesions.
The age list does not cover every case. An unusual skin mast cell tumour form is also recognised in young cats, particularly Siamese, and can sometimes disappear spontaneously. However, this cannot be reliably identified at home. Monitoring without removal, where appropriate, rests on veterinary diagnosis and agreed follow-up, rather than age or breed alone.
Typical symptoms
Skin mast cell tumours:
- One or several skin lumps.
- Lesions that may be pink, red or brownish.
- Itching, inflammation and ulcers.
- Hair loss over the tumour.
Internal mast cell tumours affecting the spleen or intestines:
- Reduced appetite and weight loss.
- Vomiting and diarrhoea, sometimes bloody.
- An enlarged abdomen and ascites.
- Pale mucous membranes and lethargy.
Appearance varies, and a lump's colour does not reliably indicate malignancy. A lesion may also shrink temporarily and later enlarge again. Inflammation and release of mast cell substances can affect swelling, so temporary shrinkage does not confirm recovery.
Abdominal symptoms can result from many diseases besides mast cell tumours. Persistent poor appetite, weight loss or vomiting needs investigation even without skin abnormalities. Also report stool colour and whether symptoms developed gradually or suddenly.
Complications and consequences
- Recurrence of the skin form after removal.
- Metastases to lymph nodes, liver and spleen.
- Severe histamine-related allergic reactions, including gastrointestinal ulcers and anaphylaxis.
- Death in generalised disease.
A histamine-related gastrointestinal ulcer is not the same as anaphylaxis. Mast cell mediators can cause different local and whole-body effects. Do not squeeze or unnecessarily handle the tumour. Sampling and any medicines to prevent symptoms are planned at the veterinary practice.
Diagnosis at the vet
- Clinical examination of suspicious lumps.
- Cytology to identify characteristic granule-containing cells.
- Biopsy and histology to confirm the diagnosis and assess malignancy.
- Abdominal ultrasound if an internal form is suspected.
- Blood tests and biochemistry to assess general health.
A cell sample is often useful for this tumour type because mast cell granules can aid recognition. A tissue sample adds information about structure and characteristics. Surgical margins are also assessed in a removed lesion. Small size alone does not reliably indicate benign behaviour.
Alongside skin examination, disease extent may be assessed through lymph node and abdominal organ samples where needed. A splenic or intestinal change on ultrasound alone does not confirm a mast cell tumour, because other diseases can look similar. Some situations need tissue sampling or surgery to refine the diagnosis.
Blood tests assess anaemia and other aspects of general health. Bone marrow sampling or broader investigations may be considered according to findings. Investigations differ for a solitary skin lump without symptoms and a cat with multiple lesions or internal organ symptoms. Prognostic information for canine mast cell tumours is not directly applied to cats.
Treatment
A solitary skin tumour is often treated by surgical removal. Surgery and sample examination also provide information about further treatment needs. If removal is incomplete, options may include another operation, radiotherapy or planned monitoring. The decision depends on characteristics and location; not every incomplete removal leads to the same next treatment.
Chemotherapy or other medicines affecting tumour growth may be considered for multiple, widespread or difficult-to-remove tumours. Product choice and possible adverse effects are discussed with your vet. Evidence is not equally strong for every medicine option, and a medicine used in dogs is not automatically suitable for cats.
Spleen removal may be central to treatment of a splenic tumour. Before surgery, the team investigates, where possible, whether disease is present elsewhere and whether your cat is fit for surgery. An intestinal tumour plan may include removing the affected bowel section and other cancer treatment. Surgery is not always possible or sufficient for widespread disease.
Your vet may also prescribe medicines to control the effects of released mast cell substances and protect the gastrointestinal tract. Do not start these yourself to enable squeezing or handling the tumour at home. Pain, nausea and eating difficulties are treated as part of overall care.
Home care and monitoring
Keep the surgical wound dry and prevent licking and scratching as instructed. Report increasing swelling, bleeding, discharge or wound opening. Use only prescribed topical products. If wound protection or medicine administration is difficult, ask the practice for another approach.
Check skin beyond the original tumour site too. A new lump may be a separate lesion or related to the previous disease; feeling it at home does not distinguish them. Record it and arrange examination. Also monitor weight, appetite, vomiting, stools and willingness to move and socialise.
If active tumour treatment does not suit your cat, symptom-relieving care can still support everyday life. Agree what makes a good day for this cat and which changes require contact. Assessment also considers the burden of handling and repeated visits.
Prognosis
Prognosis particularly depends on location, tissue findings, spread and treatment response. Many skin forms behave calmly, but there are exceptions. Splenic and intestinal tumours are not given one shared prognosis. An average survival time alone does not establish how an individual cat will respond.
Prevention
- Check an older cat's skin regularly.
- Have suspicious tumours removed promptly.
- Exclude affected animals from breeding if hereditary susceptibility is suspected.
- Support immunity and treat chronic skin inflammation promptly.
There is no known reliable prevention method. Investigating a suspicious lump is early detection, rather than a guarantee of preventing mast cell tumours. The breeding recommendation does not mean every affected cat has confirmed hereditary susceptibility; limited breed and inheritance information is considered separately. General health care does not replace sampling.
Important for cat owners
Mast cell tumours are among the most common feline skin tumours. Remember that every suspicious skin lump needs examination, preferably by a vet experienced in cancer. Even if a tumour seems benign, only cell and tissue examination can establish its nature. Skin mast cell tumours have a good prognosis after early removal, but internal forms are aggressive and require several treatment approaches.
Finding an internal tumour does not mean treatment cannot help. The potential benefit of spleen removal, for example, is assessed for each cat, and intestinal disease outcomes can also vary. Discuss a prognosis based on findings before making decisions.
This article provides general information and does not replace veterinary care. Contact a vet if you notice signs of illness in your cat.
Frequently asked questions
Is a skin mast cell tumour always malignant?
No. Many solitary skin forms behave favourably and can be treated surgically. Sampling and assessment of disease extent are still needed, because appearance cannot reliably predict behaviour.
Can a mast cell tumour affect only the spleen?
Yes. Internal disease does not always involve skin lumps. A splenic change is investigated through imaging and sampling where needed, with treatment planned according to findings.
Can a shrinking lump be left unexamined?
Do not assume it has healed. Mast cell tumour size can vary with inflammation. Even a lesion that sometimes shrinks should be shown to a vet.
Do splenic and intestinal tumours have the same prognosis?
No. Spleen removal may bring substantial benefit to a suitable patient, whereas intestinal disease is often harder to treat. Both require assessment of spread, tissue findings and overall health.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
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- Mast Cell Tumours in Cats: Clinical update and possible new treatment avenues, Journal of Feline Medicine and Surgery, accessed 2026-11-03.
- Mast Cell Tumours, American College of Veterinary Surgeons, accessed 2026-11-03.
- Care of Surgical Incisions in Cats, VCA Animal Hospitals, accessed 2026-11-03.
- 2023 AAFP/IAAHPC Feline Hospice and Palliative Care Guidelines, American Association of Feline Practitioners and IAAHPC, accessed 2026-11-03.
- Chronic Pain Assessment in Cats, American Animal Hospital Association, accessed 2026-11-03.
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