The Symptoms of Mast Cell Tumors in Dogs

By Jane Meggitt

Mast cell tumors account for approximately 20 percent of all canine skin tumors. Symptoms of mast cell tumors in dogs are fairly straightforward, as you can usually see or feel these growths on your pet. If a mast cell tumor is caught early, surgery is often curative. However, if the tumor has metastasized, or spread, the prognosis isn't good. If you notice any growths on your dog, take him to the vet as soon as possible to have the growths evaluated.

Mast Cell Tumors

Mast cells are found in dogs' connective tissue, near the skin surface. Technically known as mastocytomas, mast cell tumors are generally single growths, although they can appear in multiple masses. If a tumor is well-differentiated -- that is, has cells that resemble normal cells -- a dog might lose hair in the tumor site, but the growth rarely bleeds. Slow-growing, these tumors usually reach between 1 and 4 centimeters in size. If a tumor is undifferentiated, or has cells that don't resemble normal tissue, it might grow very fast and ulcerate, causing the animal obvious pain. The area around it might redden and contain fluid. Symptoms of internal mast cell tumors include vomiting, appetite loss and black, tarry stools.

Tumor Locations

Most mast cell tumors occur on the trunk or in the area between the anus and genitals. In females, that's between the vulva and anus; in males it's between the scrotum and anus. Other locations where mast cell tumors might develop are the legs and paws, and the neck and head. You might notice lymph node enlargement around the site of a tumor. Rarely, mast cell tumors develop internally, so you won't be able to see them. Tumors growing in the anal/genital region, nail bed, mouth or muzzle tend to have the worst prognosis.

Affected Breeds

While any dog might develop a mast cell tumor, certain breeds are more likely to do so. These include the beagle, the boxer, the Boston terrier, the bull mastiff, the English bulldog, the cocker spaniel, the English setter, the golden retriever, the Shar-Pei, the schnauzer and the Labrador retriever. Mast cell tumors appear equally in males and females; they most often appear in older canines.

Diagnosis and Treatment

Your vet will biopsy the tumor to identify the type of cells in the growth and determine the stage of the disease. She'll also perform ultrasounds and X-rays to determine the tumor's size and location. Surgical removal of the tumor is almost always indicated, along with removal of any affected lymph nodes. Your dog might also undergo chemotherapy and radiation. Your dog's prognosis depends on the tumor's grade and level of invasion.