Dr. Kim Freeman, DACVIM Oncology

Although there are some similarities between mast cell tumors in dogs and cats, there are many differences, as well. In both species, mast cell tumors are a cancerous overgrowth of a normal cell in the body called a mast cell. Mast cells are part of the immune system. They are produced in the bone marrow, but ultimately reside in many parts of the body. They are commonly found in the blood, skin, intestinal tract and spleen. As part of the immune system, they are best known for their role in allergic reactions, but also participate in the body’s defense against infections. Mast cells can release several chemicals when activated, such as histamine, heparin, seratonin, prostaglandins and other enzymes. The chemicals can have a significant effect on the body.

Mast cells play a vital role in normal allergic reactions.

In cats, mast cell cancer can present itself in three different ways:
1) cutaneous (in the skin)
2) splenic (in the spleen) or visceral (in the abdomen or abdominal organs)
3) intestinal

In this blog post, I will discuss cutaneous mast cell tumors in cats. In the United States, mast cell tumors represent about 20% of all feline skin tumors. These tumors are typically small in size and found on the surface of the skin. Often, they do not have hair growing out of them. They can be ulcerated and itchy. Sometimes they look like a small skin tag or mole. They can be white or pink in color. Siamese cats have an increased risk for getting mast cell tumors.

Fortunately, most cutaneous mast cell tumors in cats are benign. In rare circumstances, these tumors can spread to nearby lymph nodes, internal organs (liver or spleen), or bone marrow. Up to 22% of cats with a cutaneous mast cell tumor have disease in the spleen or in multiple skin sites. So, we recommend that your veterinarian do an exam to make sure there are not multiple skin bumps, enlarged lymph nodes, or an enlarged spleen. These tumors can be diagnosed on cytology. However, cytology will not tell you whether this cancer is benign or malignant. Surgery will be necessary to obtain this information. There is even a special blood test that can be done to look for mast cells in the blood. This test is called a “buffy coat analysis”. This test is unreliable in dogs, but can be quite helpful when looking for signs of systemic disease in cats. Your veterinarian may recommend an abdominal ultrasound and needle biopsy for cytology of the spleen to make sure that your cat does not have spread of the mast cell cancer to other parts of the body.

The treatment of choice for solitary cutaneous mast cell tumors in cats is surgery. These tumors do not typically require aggressive surgery to take wide margins. Often, we can cure this cancer with a small, localized surgery. If surgery is not possible, based on location, then it is advisable to consult with an oncologist for other options such as radiation therapy, chemotherapy, or treatment with corticosteroids (Prednisolone/ Prednisone), either oral or intralesional.