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Feline mastocytoma
Mastocytoma is a tumor that arises from mast cells, cells of the immune system rich in histamine, present in the skin and in several organs. In cats, it exists in two very distinct forms. The cutaneous form appears as one or more small nodu...
What is it?
Mastocytoma is a tumor that arises from mast cells, cells of the immune system rich in histamine, present in the skin and in several organs.
In cats, it exists in two very distinct forms. The cutaneous form appears as one or more small nodules in the skin, often on the head or neck, and most often behaves in a non-aggressive manner.
The internal form mainly affects the spleen and sometimes the intestine; it is more serious and results in general signs rather than a visible mass.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Cutaneous form: one or more firm nodules in the thickness of the skin, often small, whitish or pink, generally without hair at the top.
The head, neck and base of the ears are the most common locations.
These nodules can itch, redden, swell or change size from one day to the next: this is the effect of the histamine released, especially when they are handled.
Some ulcerate and bleed.
In young cats, particularly of the Siamese type, several nodules can appear together and regress spontaneously.
Internal form: depression, loss of appetite, weight loss, sometimes chronic vomiting, stomach distended by an enlarged spleen.
Black stools or difficult digestion in case of stomach ulcer.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The tumor results from an uncontrolled multiplication of mast cells.
Genetic anomalies acquired by these cells, affecting a receptor which controls their multiplication, have been identified in cats.
These anomalies appear during the life of the animal: they are neither inherited from the parents nor linked to anything that the owner would have done.
No environmental factor has been clearly established as a trigger in cats.
Age: the classic cutaneous form and the internal form mainly concern middle-aged to older cats.
A particular form, with multiple nodules and sometimes regressive, is seen in young cats, particularly of the Siamese type.
No lifestyle, diet or known exposure has been identified as a risk factor.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Any skin nodule in a cat should be identified rather than monitored indefinitely: a mastocytoma is indistinguishable from a cyst or other tumor to the naked eye.
A fine needle aspiration is most often sufficient for diagnosis: mast cells are easily recognized under a microscope. It’s a quick gesture, achievable in consultation.
The veterinarian palpates the entire body looking for other nodules, as well as the lymph nodes and the stomach.
An abdominal ultrasound is recommended to examine the spleen, liver and intestine: an internal form can accompany or explain skin nodules.
A blood test completes the assessment and can reveal circulating mast cells in advanced forms.
Laboratory analysis of the removed tumor specifies its more or less aggressive nature, which guides what happens next.
Treatment
Cutaneous form: surgical removal of the nodule is the standard treatment and is sufficient in the majority of cases. The necessary margins are generally narrower than in dogs.
When the nodules are numerous or located in places that are difficult to operate on, other options exist depending on the case, and simple monitoring is sometimes chosen for forms in young cats likely to regress.
Splenic form: removal of the spleen is the main treatment and often significantly improves the cat's condition, including when the disease is extensive.
Intestinal form: surgery is possible on a localized lesion, but this form is the most difficult to treat.
Medications that protect the stomach and block the effects of histamine are prescribed, because mast cells release it in large quantities, especially at the time of surgery.
Chemotherapy and treatments targeted at the receptor abnormality are used in extensive or inoperable forms.
The protocol is decided with the veterinarian according to the shape, the number of lesions and the general condition of the cat.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
There is no known way to prevent this tumor from occurring.
The useful lever is early detection: pass your hand over your cat's entire body once a month, paying particular attention to the head, neck and base of the ears.
Have any new nodule identified rather than observing it for months: a puncture is quick, inexpensive and avoids letting a tumor evolve which can be treated very early.
An annual general examination, with palpation of the abdomen, helps to identify an enlarged spleen before the appearance of signs.
Possible complications
Stomach ulcers caused by released histamine, with vomiting, difficult digestion and black stools.
Brutal reaction at the time of handling or surgery, linked to a massive release of histamine: the veterinarian anticipates this with preventive treatment.
Extension to the spleen, liver, lymph nodes or bone marrow in aggressive forms.
Anemia and coagulation abnormalities in advanced internal forms.
Appearance of new nodules after removal of a first lesion.
When to see a veterinarian
You discover a nodule in your cat's skin, even a small one: have it identified.
A nodule changes size, turns red, swells or itches, especially when touched.
It ulcerates or bleeds.
Your cat vomits regularly, loses weight and his stomach seems swollen.
His stools are black or tarry.
He is dejected and refuses to eat.
Prognosis
The single cutaneous form, surgically removed, has a generally favorable prognosis in cats, with an often benign course after surgery.
Recurrences or new nodules elsewhere remain possible and justify regular palpation.
The form affecting the spleen has a more guarded prognosis, but removal of the organ often brings a clear and lasting improvement in quality of life.
The intestinal form is the most aggressive and the most difficult to control.
The type specified by laboratory analysis remains the most reliable element for anticipating developments.
Frequently asked questions
A little lump in my cat's skin, should we be worried?
We should not be alarmed, but we must have it identified. A fine needle puncture is done in consultation and quickly provides the answer. Waiting several months is the only real mistake.
Why does the nodule swell when I touch it?
Because mast cells release histamine when handled, which causes localized redness, swelling and itching. Avoid fiddling with a suspicious mass.
Is cat mastocytoma as serious as dog mastocytoma?
No, the cutaneous form of the cat generally behaves less aggressively than that of the dog and surgery is often enough. Internal forms, on the other hand, require more in-depth support.
My cat has several nodules: is it more serious?
Not necessarily. In some young cats, multiple nodules regress spontaneously. In older cats, multiple nodules warrant a complete assessment, including an ultrasound of the spleen. Only the veterinarian can tell the difference.
References
AAFP — American Association of Feline Practitioners
Content reviewed by the TunisieVet editorial team · Updated 09 August 2026
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