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Mast Cell Tumors in Cats

Posted July 09, 2015 in Cat Diseases & Conditions A-Z

AJ Debiasse, a veterinary technician in Stroudsburg, PA, contributed to this article.

Mast cells are a normal part of your cat's immune system: they are a type of white blood cell. Occasionally, a mast cell can become a tumor, logically called a mast cell tumor. There are two types:

  • Those that affect the skin (cutaneous mast cell tumors)
  • Those that affect internal organs (visceral mast cell tumors)

Maine coon cat sitting on couchMast cell tumors of the skin (cutaneous)
Approximately 20% of skin masses in cats are cutaneous mast cell tumors, and about 90% of those are benign. External skin mast cell tumors generally form on the head, neck and body, but can be anywhere. They are small, firm, raised, hairless and can become itchy. Some cats will cause self-trauma by itching and chewing during these flare-ups.

Mast cell tumors of internal organs (visceral)
Up to half of all mast cell tumors are visceral, and they most commonly affect the spleen. They can also affect the intestine. Visceral mast cell tumors can cause lethargy, a decreased appetite, weight loss or vomiting.

Is my cat at risk of mast cell tumors?
Any cat can be affected by mast cell tumors, but it seems more common in felines over 4 years of age. There is a higher incidence in Siamese cats.

Diagnosing mast cell tumors in cats
To diagnose a mast cell tumor, a fine needle aspiration (FNA) is usually performed. A small needle is inserted into the mass, cells are drawn out, placed on a glass slide and evaluated under the microscope. This is called cytology.

For skin masses, sedation is not usually required. For internal masses however, ultrasound guidance and sedation may be required to obtain a sample safely and painlessly. To determine the severity of the disease, blood work, a special blood test (“buffy coat”), a bone marrow test, X-rays and/or an ultrasound of the belly may be recommended.

Manipulation of mast cell tumors, for example, when obtaining samples, can cause the release of chemicals (such as histamine) stored in the cells. This can cause all kinds of problems. To prevent these problems, your vet will likely give an antihistamine medication prior to sample collection or tumor removal.

Treating mast cell tumors in cats
Surgery, followed by a biopsy, is the recommended treatment for both cutaneous and visceral mast cells tumors. Most commonly, this requires removing a mass on the skin or removing the spleen.

Surgical recovery takes an average of 2-4 weeks of restricted activity, confinement and a plastic cone (Elizabethan collar). Antibiotics, pain medications and antihistamines are continued at home. Additional treatment, such as chemotherapy, will depend on the biopsy results.

Cats with cutaneous mast cell tumors typically do very well. The tumors are not very likely to come back after surgery. It can be curative. Most cats live many years post surgery.

Cats with visceral mast cell tumors often don't have so good an outcome, but live an average of a year with “combination therapy,” (i.e. surgery, chemotherapy and supportive care). Cats with a mast cell tumor in the spleen typically do much better than cats with a tumor in the intestine. The outcome worsens even more if spreading or metastasis is present.

Overall, mast cell tumors in cats are “good” in the skin and “bad” in the belly. It is very important to work closely with your family vet, your surgeon and/or your oncologist to obtain the best possible outcome.

If your cat has a mast cell tumor, here are some questions to ask:

  • How do we determine if it’s benign or cancerous?
  • How do we make sure it hasn’t spread?
  • What is the best treatment?

If you have any questions or concerns, you should always visit or call your veterinarian -- they are your best resource to ensure the health and well-being of your pets.

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Dr. Phil Zeltzman is a board-certified veterinary surgeon and author. His traveling practice takes him all over Eastern Pennsylvania and Western New Jersey. You can visit his website at www.DrPhilZeltzman.com, and follow him at www.facebook.com/DrZeltzman.