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Canine mastocytoma

Mastocytoma is the most common malignant skin tumor in dogs. It develops from mast cells, skin cells responsible for releasing histamine during allergic reactions. Its particularity is that it takes on all appearances: small hard lump, soft...

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Definition Signs Causes Diagnosis Treatment Prevention Complications When to see a vet Prognosis FAQ Sources Affected species

What is it?

Mastocytoma is the most common malignant skin tumor in dogs. It develops from mast cells, skin cells responsible for releasing histamine during allergic reactions.

Its particularity is that it takes on all appearances: small hard lump, soft mass mistaken for a lipoma, red patch, wart, hairless area. This is why he is nicknamed the “great imitator”.

There is no aspect that allows us to tell with the naked eye that a mass is a mastocytoma: only the examination of the cells tells us so.

Key point

No skin mass can be classified as “benign” to the naked eye, regardless of its appearance. A fine needle puncture costs little, is done in consultation, and avoids letting a tumor grow that would have been easy to remove.

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:

Nodules under the skin Swelling Itching Scabs and skin lesions Vomiting Loss of appetite Swollen lymph nodes

One or more masses on or just below the skin, varying greatly in size and appearance.

Mass whose size changes from one day to the next, swelling then deflating: this fluctuating behavior is characteristic, it is due to the release of histamine.

Redness, warmth and itching around the mass, especially after handling.

Ulceration of the skin above the mass, crusting, bleeding.

Neighboring lymph node enlarged.

Vomiting, loss of appetite, black stools: signs that the histamine released is irritating the stomach, to be taken seriously.

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 arises from a mast cell that has become abnormal, which multiplies and releases large quantities of inflammatory substances, including histamine.

Abnormalities of a gene involved in cell multiplication are found in some affected dogs; their research can guide treatment.

The triggering factors are not known, and nothing in the care given to the dog is in question.

Predisposed breeds: Boxer, French Bulldog, Pug, Labrador and Golden Retriever, Boston Terrier, Shar Peï, Beagle.

Middle to advanced age, although young dogs may be affected.

Dogs who have already had a mastocytoma are more likely to develop others in other places: this does not mean that the first one was poorly treated.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

The veterinarian examines the entire surface of the skin, not just the reported mass, and palpates the lymph nodes.

Fine needle aspiration is the central examination: quick, not very painful, can be carried out in consultation, it identifies mast cells with good reliability.

Once the tumor is removed, laboratory analysis (histology) specifies its grade, that is to say its degree of aggressiveness. This information conditions everything that follows.

An extension assessment may be proposed: puncture of the neighboring lymph node, ultrasound of the abdomen, blood test.

Simple rule to remember: any skin mass in a dog deserves to be punctured rather than monitored blindly.

Treatment

Surgery is the standard treatment. She removes the mass with a margin of healthy tissue around it, which explains a scar that is often much larger than the lump itself: this margin is essential to avoid regrowth.

Analysis of the operated part indicates whether the removal was complete and what the grade of the tumor is. A second surgery is sometimes proposed if the margins are insufficient.

Medications that block the effects of histamine are given around the procedure to protect the stomach and limit reactions.

Depending on the grade and extension, chemotherapy, targeted treatments or radiotherapy are considered in addition.

Low-grade mast cell tumors, completely removed, are often resolved with surgery alone.

Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.

Prevention

There is no prevention of the appearance of a mastocytoma.

Useful prevention is that of delays: pass your hands all over your dog's body once a month, note the location and size of the masses found, and show them to the veterinarian.

In predisposed breeds, report any new lumps without waiting for the annual visit.

Never squeeze, scratch or handle a suspicious mass for a long time: this can trigger a release of histamine and a significant local reaction.

Possible complications

Ulceration and infection of the mass, painful and difficult to heal.

Stomach ulcers linked to excess histamine, manifested by vomiting, loss of appetite or black stools.

Sudden and significant swelling after manipulation of the tumor.

Diffusion to lymph nodes, spleen, liver or bone marrow in high-grade forms.

Appearance of new mastocytomas in other places in the body.

When to see a veterinarian

You discover a new lump on or under your dog's skin, even if small and painless.

A known mass changes size, color, turns red, or begins to itch.

The mass ulcerates, bleeds or oozes.

Your dog vomits, stops eating or makes very black stools even though he has a skin mass: seek medical attention quickly.

Significant swelling appears around the mass after touching it.

Prognosis

The prognosis depends above all on the grade of the tumor and the quality of surgical removal.

Low-grade forms, removed widely, are frequently cured and do not subsequently affect the dog's life.

High-grade forms are more aggressive and require heavier support, with close monitoring.

This variability explains why the veterinarian cannot make a decision before having the laboratory report: it is this document which gives the true level of risk.

Frequently asked questions

Why is the scar so big for a small ball?

Because mast cell cells extend into the tissue far beyond what we see and feel. The surgeon therefore removes a margin of healthy skin all around and in depth. This margin is the best guarantee against regrowth in the same place.

This mass inflates and deflates on its own, is that reassuring?

No, on the contrary it is a fairly typical sign of mastocytoma, linked to the release of histamine. A mass with a variable volume must be shown without delay.

My dog has already had one, will he have one again?

It's possible: some dogs develop several mastocytomas during their life, in different locations. This is not to say that the first one was treated badly. A regular examination of the skin allows them to be taken early, when the surgery remains simple.

Should we operate even if the lump does not bother him?

A painless mass may well be a mastocytoma. The decision is made after the puncture: if the cells are mast cells, removing it while it is small is much simpler and safer than waiting for it to grow.