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208 Breeds, 422 Health Conditions  |  Find a Vet

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Mast Cell Tumors (Mastocytomas)




Condition Overview

Mast cell tumors are common, accounting for 10 - 20% of skin tumors in dogs. About 1/2 of them are malignant. Brachycephalic breeds, such as Boxers, Boston Terriers, and Bulldogs, have a higher incidence. However, mast cell tumors can occur in any dog.


Both sexes are equally affected. Multiple tumors are present in 10% of cases. Look for these tumors on the skin of the trunk and perineum, lower abdomen, foreskin of the penis, and hind legs.

Mast cell tumors vary greatly in appearance. The typical tumor is a multi-nodular that appears reddish, hairless, and ulcerated. Some growths may be present for months or years, then suddenly enlarge and metastasize to regional lymph nodes, liver, or spleen. Others grow rapidly right from the start. Still others may be completely under the skin and look like lipoma.


In Bernese Mountain Dogs, mast cell tumors are especially common and are inherited as a polygenic trait. The mean age for dogs to develop mast cell tumors is 9 years.

Mast cell tumors release histamine and other substances that cause stomach and duodenal ulcers. In fact, up to 80% of dogs with mast cell tumors may be suffering from ulcers. Dogs with intestinal symptoms should be evaluated for ulcer disease and treated accordingly.


All new lumps should be checked by your veterinarian. It is impossible to tell by appearance whether the tumor is benign or malignant.


The World Health Organization has established a system for staging mast cell tumors based on the size of the tumors, the number present, the degree of local involvement, and the presence or absence of metastases.

Early stage (favorable) tumors are treated by complete local excision with a margin of normal tissue. Larger tumors that cannot be removed with adequate tissue margins are treated with surgery plus prednisone and/or radiation therapy. Chemotherapy and/or immunotherapy have been of benefit in treating late-stage disease.


There is no prevention for this condition.


Please contact your veterinarian if you have questions regarding this condition.

Show Sources & Contributors +


Dog Owners Home Veterinary Handbook

Publisher: Wiley Publishing, 2007

Website: http://www.wiley.com/WileyCDA/

Authors: Debra M. Eldredge, Liisa D. Carlson, Delbert G. Carlson, James M. Giffen MD

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