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Mast Cell Tumors in Cats

Mast cell tumors are common in cats.

Mast cells are a type of white blood cell. They normally function as part of the immune system, reacting to foreign invaders. When they multiply abnormally, they can form tumors. Mast cell tumors in cats may either be on the skin or within an organ in the body.

How Dangerous Are Mast Cell Tumors in Cats?

Mast cell tumors (MCT) range from non-malignant to very malignant. In general, MCT found on the skin of cats are more likely to be benign while MCT in internal organs is often malignant and behaves aggressively.

Cats diagnosed and treated for cutaneous (skin) MCT often do well and live for years. However, those with internal MCT have a worse prognosis. There are treatments that can help cats live for a year or more with visceral (organ) MCT, but that form of the cancer is usually aggressive.

MCT is the second most common skin tumor, most common splenic tumor, and third most common intestinal tumor in cats.



Signs of Feline Mast Cell Tumors

The signs of MCT in cats depend on whether it is the cutaneous or visceral form.

The cutaneous form of MCT may cause the following signs:

  • Round, hairless, raised bump or bumps on the skin that may not seem to bother the cat or may cause intermittent licking and chewing of the area.
  • Mast cell tumors of the skin may wax and wane in size. This is because the mast cells that make them up can be volatile. Since their normal job is reacting to bodily invaders, they are touchy, and can mount an allergic reaction if they're bothered.

The visceral form of MCT in cats may cause the following signs:

  • Decreased appetite
  • Weight loss
  • Vomiting
  • Lethargy

Diagnosis of Mast Cell Tumors in Cats

A fine needle aspirate (FNA) may be done on a cutaneous lesion. Cells that are gathered from the test can be examined under a microscope to identify cancerous mast cells.

For internal cancer, blood work, x-rays, ultrasound, CT scan, and/or surgical biopsy may be required for diagnosis.

Mast Cell Tumor Treatment for Cats

Treatment of MCT of the skin in cats means surgical removal of the lesion. The surgeon will remove as much of the skin around the bump as possible, as well, because there may be cancer cells in that area, and leaving them might result in recurrence.

Once removed, the lesions should be sent to the lab for a pathologist to examine. This will help determine the malignancy of the MCT as well as whether further surgery is required to remove more tissue in the area.

Visceral MCT is not usually treated surgically unless the involved organ is the spleen; in that case, splenectomy may be performed. Otherwise, chemotherapy is the preferred treatment at this time, and your cat may be referred to a veterinary oncologist.

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