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Mast-Cell Tumors

General Information

Mast-cell tumors occur in both dogs and cats and may be either non-cancerous (benign) or cancerous (malignant). In general the tumors in cats are usually benign while the tumors in dogs should always be considered potentially malignant. Their cause is unknown, and they occur more frequently in Boxers, Boston Terriers, English Bulldogs, Bull Terriers, Fox Terriers, Labrador Retrievers, Dachshunds and Weimaraners than in other breeds. Most dogs are middle-aged when affected. When the tumor is removed that pathologist usually can tell us what percentage chance of malignancy to expect of the tumor type. Chemotherapy may be done if the tumor recurs. Chemotherapy for mast cell tumors does not cure the tumor but probably improves the time and quality of life in dogs with recurrance of the tumor. It is also fairly inexpensive. The primary tumor should generally always be removed first.

Mast-cell tumors vary widely in shape and size, but they are usually single tumors in dogs and multiple tumors in cats. In dogs, they occur most frequently on the trunk, limbs and anal region. Malignant growths in dogs are frequently located between the toes. They are usually easy to identify by cytology on a fine needle aspirate.

Important Points in Treatment

1. Mast-cell tumors should be surgically removed as soon as possible, since many are malignant.

2. Irradiation and/or chemotherapy are recommended when mast-cell tumors are advanced or cannot be completely removed. Your doctor will advise you if your pet should receive this type of therapy.

3. Surgical patients:

Check the incision site at least once daily. Report any abnormalities to the doctor. Restrict your pet's activity for ____ days. Prevent your pet from licking or chewing at the incision. Please call the doctor if this is a problem. Your pet will be evaluated for suture removal in ____ days.

Notify the Doctor if Any of the Following Occur:

* Your pet develops new growths.

* Your pet damages the incision or removes any sutures.

* Your pet's general health changes.

Understanding Your Pet's Medical Diagnosis


What are mast cell tumors?

Mast cells are found throughout the skin, spleen, and gastrointestinal (stomach and intestines) tract of the dog and cat. Mast cells are connective tissue cells that contain histamine and heparin. Release of histamine and other substances results in local swelling, inflammation, and irritation. A mast cell tumor is a tumor of these specialized cells. Mast cell tumors are found in dogs and cats. Mast cell tumors generally are found in the skin of dogs. They represent 25% of all skin tumors in dogs. Mast cell tumors are the fourth most common tumor type in the skin of cats. Mast cell tumors also are found in the spleen and intestines in cats.

What causes mast cell tumors?

The cause of mast cell tumors is unknown.

What are the signs of mast cell tumor?

The clinical signs associated with a mast cell tumor vary, depending on the location and stage of the tumor. The skin is the most common system affected in dogs, with most tumors developing over the limbs and trunk region. In such cases, one or multiple skin masses may be present. The masses may appear red and swollen. The spleen is a common primary location for mast cell tumors in cats. The clinical signs associated with mast cells tumors of the spleen include lack of appetite, enlargement of the spleen, anemia (decreased number of red blood cells), and ulcers of the stomach and small intestine. Lymph nodes may be enlarged in the dog or cat if the mast cell tumor has spread (metastasized) to other parts of the body. The animal may vomit.

How are mast cell tumors diagnosed?

Mast cell tumors are diagnosed by physical examination and tests to identify the type of tumor. Mast cell tumors can be diagnosed through a biopsy (surgical removal and microscopic examination of a tissue sample from a suspected tumor). The results of histopathological evaluation of the biopsy confirm the diagnosis of mast cell tumor and allow for staging of the tumor. Staging of tumors is important for prognosis. Staging the mast cell tumor provides information regarding the extent of disease and aids in the selection of appropriate treatment. Radiographs (X-rays) of the chest and abdomen may be performed to look for evidence of tumor growth in other organs of the body. Blood work also may be performed to determine the presence of anemia and assess the animal's overall health status.

How are mast cell tumors treated?

Surgical removal is the treatment of choice for mast cell tumors in dogs and cats. Radiation therapy can be performed when the tumor cannot be removed completely. In cases where neither surgery or radiation therapy is adequate, chemotherapy is another option. Drugs that prevent the release of histamine from mast cells may be prescribed.

What is the prognosis for animals with mast cell tumor?

The prognosis (outcome) for animals with mast cell tumors is guarded. The prognosis depends on the location and extent of the tumor(s), the grade of tumor, and the type of therapy chosen for the patient. Mast cell tumors in dogs are graded I to III, with grade III being the most aggressive tumor. Survival times for dogs with mast cell tumors vary, depending on the grade of the tumor. Approximately 75% of dogs with grade I tumors will survive for at least 6 months after surgery while only 45% of dogs with grade II tumors and 13% of grade III tumors will survive for at least 6 months after surgery. A similar grading system has not been established for cats.

An animal that has had more than one mast cell tumor of the skin is likely to develop new tumors. The pet guardian needs to check the pet frequently and to have any new masses evaluated by a veterinarian as soon as possible. Animals with mast cell tumors may have complications, such as excessive bleeding (secondary to the release of heparin) or stomach problems (secondary to the release of histamine).

The information on this page was obtained from the site www.vetmedcenter.com