A mast cell tumor* (mastocytoma) is a potentially very malignant tumor of mast cells in the skin. This tumor is the most common skin tumor in dogs. It mainly occurs in the skin but not only there. A mast cell tumor can look very different. The tumor can be in the skin or under the skin. The presentation is usually like a solitary solid (sometimes soft) bump with a diameter of a few mm to as much as 10 cm. The overlaying skin is often alopecia (bald spot), erythematous (abnormal red), sometimes eroded or ulcerated (open wound). One should not squeeze the tumor; histamine granules* can be released (degranulate) This can cause an anaphylactic reaction, which means that the animal can get into shock. As mentioned, the tumor can be red in color, contain extra pigment or have the normal color of the skin.
As with all bumps on the skin, it is never possible to determine on the outside whether there is a tumor and what kind of tumor it is. Therefore, further investigation must also be carried out in the event of a suspicion of a mast cell tumor. This can be done by means of a FNAB (Fine Needle Aspiration Biopsy) or by means of a tissue biopsy. Cells are taken from the bump and these cells are assessed under the microscope (by a cytologist) as in this case. A FNAB gives a correct diagnosis in a large number of cases, but in all cases a tissue biopsy gives a correct and sometimes more extensive diagnosis.
The most important treatment for a mast cell tumor is ample surgical removal (margins of at least 3 cm!) Moreover, it is advisable to examine the surrounding lymph nodes for possible metastases. If extensive and complete removal is not possible or the tumor returns quickly, a mast cell tumor can be treated with radiation, medication or chemotherapy. Unfortunately the chance of a cure is limited then.
© www.willemsmicroscope.com
With thanks to Cees Koopman, veterinarian and cytologist.
*Mast cell: tissue cell of the immune system
*Histamine: chemical which triggers the immune system.
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