Mast Cell Tumors
Joe Bodewes, DVM
Veterinary Services Department, Drs. Foster & Smith, Inc.
Canine mast cell tumors account for up to 20% of all skin tumors in dogs. While they often appear small and somewhat insignificant, they can be a very serious form of cancer in the dog. Some mast cell tumors are easily removed without the development of any further problems and others can lead to a life threatening disease. Proper identification and treatment are very important in controlling this disease.
Which dogs are at risk for developing mast cell tumors?
Mast cell tumors can develop in all ages and breeds of dogs. They are very rare in cats and humans. There appears to be a hereditary factor to these tumors as shown by some strong breed predilections. Dachshunds, English Bulldogs, Fox Terriers, and Staffordshire Terriers are all at increased risk. Boxers and Boston Terriers are at even higher risk and appear to have certain genes that make them more susceptible to the disease. One study has indicated that younger dogs that develop mast cell tumors are not as likely to develop the more severe forms of the cancer.
The exact cause of mast cell tumors is still speculative. A viral source has been mentioned, as well as hereditary and environmental factors. It is quite possible that there are a variety of different causes for the development of this tumor. Because this tumor is not found in humans, there has not been as much research and information available for the veterinarian as there are for tumors that are found in both humans and animals.
What are the symptoms of mast cell tumors?
The appearance of mast cell tumors can be widely variable. They can be either benign or malignant and can be found on any part of the body. They are found most commonly on the trunk, limbs and perineal (genital) area. Tumors can be found on the skin or in the underlying or subcutaneous tissue. They can be single or multiple and can be smooth, bumpy or even ulcerated. As you can see, they come in a variety of shapes and locations so a good diagnostic workup is necessary to properly identify a growth as a mast cell tumor.
Because of the large amounts of histamine, heparin and proteolytic enzymes (enzymes which break down protein) present in mast cell tumors, they can create problems when damaged or removed. Sites where the tumors are removed can sometimes refuse to heal and can become difficult to manage. There can also be systemic signs, such as vomiting and duodenal ulcers, that result from the release of these substances from the active mast cell tumors.
How are mast cell tumors treated?
Mast cell tumors are usually treated by surgical removal. It is important that the tumor is carefully removed and a large area of 'healthy' tissue around the tumor is also removed. In some cases surgical removal may not be an option. With surgical removal it should be noted that in up to 50% of the cases the tumor might regrow. Radiation therapy after surgical removal appears to be beneficial and may reduce the incidence of reoccurrence and increase survival rates. When dealing with mast cell tumors and their wide variety of forms, it is important to remember that each animal needs to be evaluated and treated individually.
Conclusion
Mast cell tumors can present in a wide variety of ways and can have an equally varied set of symptoms and outcomes. Because it is difficult to diagnose a mast cell tumor by visual inspection, it is important that all suspicious looking skin tumors be examined by a veterinarian and followed up with diagnostic testing and identification. Treatment consists of surgical removal and radiation. As with all tumors, prompt recognition and treatment is very important in obtaining the best possible outcome.
References
Bonagura, J. Current Veterinary Therapy 12. Published by WB Saunders. Philadelphia; 1995.
Ettinger, S. Textbook of Veterinary Internal Medicine. Published by Saunders. Philadelphia; 1989.
Vail, D. Dealing with Canine Mast Cell Tumors. Veterinary Product News. December 1999.
Piscopo, S. Canine Mast Cell Tumors. Veterinary Forum. June 1999.
