Feline Mast Cell Tumor

Feline mast cell tumor is the second most common type of tumor in cats and is found on the skin (cutaneous), in the spleen, liver and abdomen . Tumors can be benign (not cancerous) or malignant (cancerous and spreads to other parts of the body). Over 90% of tumors are benign (not dangerous).

Tumors usually occur in older cats and in some instances can occur on the skin and internally.

All cells in the body that come in contact with the outside world contain mast cells. When functioning normally, the cells attack foreign bodies such as parasites. When something goes wrong with the cells, such as when they detect something that appears to be a parasite the cells react causing an allergic reaction. Similarly, when mast cells aren't reacting properly they form tumors both inside and outside of your cat's body.

Your veterinarian will need to do an examination to determine if a tumor is due to temporary inflammation of the skin or something more serious such as skin cancer.

They are found in every area of the body with most tumors located on the head and neck.

Diagnosis of Feline Mast Cell Tumor

There are several tests that will help your veterinarian determine the type of tumor your cat is suffering from:

Blood Tests: These tests determine the basic functioning of the body and organs that help clean the blood such as the liver and kidney. Testing will look for mast cells in the blood itself which indicates that they are spreading. Low red blood cell counts could also indicate a problem with the mast cells.

Bone Marrow Tests (buffy coat test): By looking at white blood cells an evaluation can be done to see if there are mast cells present. Cells can be checked to see if they are spreading throughout the body.

Lymph Node Aspiration: In this test a needle is used to take a sample from the lymph node. Since the blood travels through the lymph system, the lymph nodes closes to the points of disease will have some mast cells present. These lymph nodes may even be swollen if the disease has progressed.

Examination of the Spleen: Your veterinarian can use x-rays to see the spleen and determine if it is enlarged. A chest x-ray can capture a wide variety of lymph nodes which can be checked for inflammation. The spleen will be examined the same way.

Treatment of Feline Mast Cell Tumor on the Skin

Treatment options for mast cell tumors in cats include surgery, chemotherapy and a type of surgery called cyrosurgery (freezing the tumor to kill the diseased tissue). After surgery, radiation might be recommended to be sure that any remaining cells are killed.

If the tumor is benign, then surgery can provide a complete cure since the diseased skin is completely removed. Another form of surgery, Cryosurgery, can also be effective and may be an option.

A newer approach is to use a chemotherapy ointment on the skin called CCNU or the brand name (Lomustine®). Recent studies on cats show that some cats respond well to this treatment.

If the tumor is benign, surgery should be a complete cure. In approximately 15% of cases a tumor will reappear.

Mast Cell Tumors in the Spleen and Abdomen
(Feline Visceral Mast Cell Tumors)

Symptoms of mast cell tumors that are impacting internal organs are vomiting, loss of appetite and weight loss.

Surgery is also used for mast cells in the spleen. A spleen is done which completely removes this organ. Cats that have received the surgery survive up to 19 months.

If the mast cell tumors are in the abdomen , then the prognosis is not good. Surgery might be tried, however, the disease can spread quickly, making surgery not effective. If your cat is eating normally or near normal when diagnosed, usually have a good prognosis/survival time of up to 19 months or more. Cats having trouble eating may only live another 8 weeks.


Kenneth M. Rassnick, DVM, DACVIM
College of Veterinary Medicine
Cornell University, Ithaca, NY

Current Therapy for Mast Cell Tumors
D. Simon
University of Veterinary Medicine, Hannover, Germany


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