Mastocytoma is a tumor that in dogs and cats has a primarily cutaneous or subcutaneous presentation, although it can also be visceral and very rarely in the form of leukemia. It is derived from cells called mast cells that are involved in inflammation, rejection of parasites, allergies... The interior of these cells is made up of granules with a multitude of bioactive substances, heparin, histamine, fundamental necrosis factor x, proteases...


Dermal and subcutaneous lesions can simulate or resemble any other lesion and in the most benign cases they can even be present for years. The clinical signs may be influenced by the release of histamine, heparin and vasoactive substances that are in your lymph nodes and they become inflamed. Some mast cell tumors can ulcerate, others become acutely inflamed and then return to their initial state due to the action of the substances contained in their lymph nodes, this is known as “Darier's sign”. There may also be gastrointestinal ulceration due to the distant effect of histamine.

When to consult

You should make an appointment with your veterinarian whenever your dog or cat has a skin or subcutaneous lesion, especially if it shows signs of inflammation, even if they are episodic.


It is the most common skin tumor in dogs and is more common in advanced age. There are certain breeds that are predisposed and this suggests an underlying genetic cause. However, the real cause is still unknown.


Most occur in the dermis and subcutaneous and are usually solitary, although they can also be multiple. In visceral mastocytosis, lymph node, liver and spleen are usually affected and is usually preceded by some aggressive solitary lesion.


Normally we diagnose mast cell tumors by clinical history and by “cytology”, which is very useful in this tumor. To know the degree of aggressiveness, we generally have to resort to a biopsy. There are immunohistochemical markers that can be useful both to confirm that it is a mast cell tumor and to know its degree of aggressiveness and to identify mutations that help us in treatment. In most cases, additional tests may be necessary: complete analysis, ultrasound, x-ray, urinalysis...


In the treatment of mast cell tumor we should first ask ourselves if we can operate. When it is compatible with surgery it is the first option. Radiotherapy, chemotherapy and targeted therapies are other useful options, even combinations between them can be used, sometimes felt necessary to improve results. In very specific cases, electrochemotherapy and a new drug, tiginalol toiglate (stelfonda) are options for treatment.
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