Mastocytoma in dogs

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Mastocytoma is a malignant tumor, usually cutaneous or subcutaneous, caused by the proliferation of certain types of cells of the immune system, present in the connective tissue of the skin, mast cells.

These cells produce multiple chemicals, some of which are involved in the mechanism of inflammation, such as histamine, or coagulation, such as heparin.

It is a very common skin tumor in dogs (about 20% of skin tumors).

How does a mastocytoma present?

In most cases, mastocytoma in dogs involves the skin. This tumor develops mainly on the trunk, less frequently on the limbs or on the head or neck.

Its presentation is very variable: it is most often in the form of a nodule, sometimes ulcerated, round, glabrous (hairless) of pink color, which can swell or become redder when handled. It can be itchy on your dog. It can also be in the form of a large, poorly defined mass, an inconspicuous thickening of the skin, many small nodules scattered all over the body.

These tumors can behave aggressively, that is to say have the capacity to spread, from the skin, to other organs (lymph nodes or ganglia, spleen, liver, lung, bone marrow, etc.): we are talking about metastases.

More exceptionally, there are “visceral” mastocytomas, the starting point of which is damage to certain organs, such as the liver, spleen or lymph nodes, and not the skin.

In the margins of this tumor, visible on clinical examination, disorders associated with the secretion of histamine and heparin are occasionally observed. They result in ulcers of the digestive tract (stomach, intestine) manifested by vomiting or abdominal pain, or by various bleeding (during surgery for example).

Which dogs are affected by mastocytoma?

Affected dogs are, on average, 9 years old, but young subjects, regardless of sex, can be affected.

Certain breeds are specially represented such as Boxers, brachycephalic breeds (such as Bulldogs), Terriers, Spaniels or even Retrievers.

How to diagnose and manage this tumor?

The presence of a single or multiple skin “mass”, possibly accompanied by an increase in the size of the lymph nodes near the lesion as well as vomiting or diarrhea, should prompt the implementation of additional examinations and appropriate therapy, without delay.

The first step is to confirm the mastocytoma; three methods exist for this:

  • fine needle aspiration which consists of inserting a small needle into the mass in order to take a micro fragment: if your veterinarian is equipped, he can stain the sample in order to look at it under a microscope. This maneuver is painless and allows you to have the result quickly (or a few minutes or a few days if the sample is sent to a laboratory)
  • a biopsy: this consists of taking a larger fragment which will be sent to a specialized veterinary analysis laboratory. This sample requires a short tranquilization or anesthesia of your animal. It is carried out when the cyctopunction is impossible to do or if it does not allow a conclusion.
  • surgery to remove the nodule (s).

Depending on the results obtained, your veterinarian may offer you:

  • to remove the tumor surgically;
  • to carry out an extension assessment: i.e. check whether the tumor has spread to other organs (lymph nodes, spleen, liver, bone marrow, etc.): for this, other punctures, ultrasounds or x-rays may be indicated.

A rigorous approach is essential in order to adapt the treatment to the mast cell tumor that your dog presents.

Indeed, it is necessary to take into account:

  • the “grade” of the mastocytoma, which is given by the analysis of the removed mass:
    • grade 1 (not very aggressive), 2 or 3 (very aggressive) according to the grading of Patnaïk
    • low grade or high grade depending on the Kiupel grading
  • the “stage” of the mastocytoma, which is given by the extension assessment (localized or metastasized tumor).

The surgical intervention consisting in removing the tumor is the appropriate treatment as soon as the diagnosis is made: it must be broad in order to avoid as much as possible the risks of local recurrence. In some cases, surgery is not possible (too large or poorly localized tumor): chemotherapy may sometimes be possible to reduce the size.

When the extension assessment reveals the presence of metastases, radiotherapy and / or chemotherapy must complete the surgical procedure.

The chemotherapy protocols (drugs used, treatment by injection or tablets, number of sessions, frequencies, medical monitoring, etc.) will be adapted and discussed with your veterinarian depending on the type of tumor, its extension, the cost and the quality of your pet’s life.

What is the future of a dog with mastocytoma?

The prognosis will, of course, be very different from one case to another. It may be favorable if it is a single tumor grade 1 (survival at 4 years was 93% then) or low-grade (95% survival at 45 months) with a complete surgical resection

It will be much more reserved, or even bad, for grade 3 tumors (6% survival at 4 years) or high grade (0% survival at 20 months), a fortiori if metastases are already present at the time of diagnosis (average of 1-3 months of survival if the liver or spleen is affected).


Mastocytoma in dogs is a formidable tumor, often underdiagnosed or diagnosed late, the management of which is complex and must call for appropriate diagnostic and therapeutic techniques.


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