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Mast Cell Tumors in Dogs and Cats


What are Mast Cell Tumors?

Mast cell tumors in dogs and cats are common skin tumors and may range from simple skin nodules to multiple, ulcerated nodules that spread to regional lymph nodes and other areas of the body. Mast cells are important cells in your pet's immune system that function in allergic and inflammatory reactions. When these cells grow abnormally, cancer in various organs may develop. These cancers are most commonly seen in the skin, digestive tract, lungs, nose, and mouth. Sometimes these cells release inflammatory chemicals that lead to a wide variety of symptoms. The presentation of these cancers may vary from benign nodules to highly malignant growths that may spread to the spleen or liver, and possibly throughout the body. These tumors may represent up to 20% of all skin tumors in dogs and cats. Internal organ involvement of the spleen and intestines is more common in cats than in dogs.

Pet Breeds Most Likely to Develop Mast Cell Tumors

Mast cell tumors appear to be more common in Siamese cats. In dogs, mast cell tumors are common in Labrador and Golden Retrievers, Mastiffs, Boxers, Bulldogs, Pugs, Boston Terriers, Rhodesian Ridgebacks, Beagles, and Pitbull Terriers.

Mast cell tumors appear to be common in Siamese cats. Any unusual growth or lump on your pet's skin should be examined by your veterinarian as early as possible.
Key Facts of Mast Cell Tumors in Dogs and Cats
  • Signs of pets with mast cell tumors include the appearance of nodules on physical exam, and other more generalized signs such as loss of appetite, vomiting, black tarry stools, digestive tract ulceration, and the development of edema and swelling.
  • Mast cell tumors may be tentatively diagnosed by needle aspiration, but tissue biopsy is necessary to grade the tumor.
  • Treatment of mast cell tumors most commonly involves surgical removal, however chemotherapy, radiation, and targeted therapies may also be used.
  • Prognosis of mast cell tumors depends on tumor location, size, ease of surgical removal, and tumor grade.



Symptoms of Dogs and Cats with Mast Cell Tumors

Mast cell tumors often appear as single or multiple raised lumps on your pet's skin. They may appear as wart-like nodules, soft lumps under the skin or ulcerated masses that may appear on multiple areas of the body. In cats, the head and neck are the most common areas affected, while in dogs the masses are most commonly seen on the trunk and the limbs. If the mast cells release inflammatory chemicals, other more generalized symptoms may occur including loss of appetite, digestive tract ulceration, vomiting, black stool, abdominal pain, widespread inflammation, and edema (buildup of fluid in tissues).

Diagnosis of Mast Cell Tumors in Pets

Initial CBC/chemistry blood tests and urine analysis are recommended to assess the overall health of your pet. Initial tentative diagnosis is often made by fine needle aspiration of the mass or masses. If possible, aspiration of the regional lymph nodes is done to assess if any metastasis (spread) of the cancer has occurred. Buffy coat smears may be done to determine if any cancerous mast cells are present in the circulation. An abdominal ultrasound is also frequently done to determine if any spread to the spleen or intestine has occurred. Definitive diagnosis requires a biopsy sample so that the cancer may be appropriately staged and a proper treatment regimen started. CT scans may offer additional diagnostic information, depending on the site of the primary cancer.



Treatment Options for Dogs and Cats with Mast Cell Tumors

Treatment of mast cell tumors will depend on the grade of cancer found through surgical biopsy, as well as the presence of any digestive tract symptoms. For most low-grade mast cell tumors of the skin, surgical removal remains the treatment of choice. In intermediate or high-grade mast cell cancers, or those where complete surgical removal is not possible, radiation and/or chemotherapy may also be done, depending on tumor location. Targeted therapies have recently been developed, including drugs known as Palladia by Pfizer and Masivet by AB Science. These more novel therapies seem to improve response and remission in dogs with intermediate and high-grade mast cell tumors. Surgery alone may be curative in many forms of feline mast cell tumors There is not much information on the use of other therapies, including chemotherapy or targeted cell therapy in cats. Anti-nausea drugs including Famotidine may be needed in pets exhibiting vomiting and/or dark tarry feces.

Prognosis for Dogs and Cats with Mast Cell Tumors

Prognosis for pets with mast cell tumors depends on your pet's age, symptoms, tumor size, location, and grade. Low to intermediate-grade mast cell tumors have a much better prognosis in dogs with surgery alone and/or surgery with targeted therapies or chemotherapy. Most dogs with high-grade mast cell tumors will die within one year of diagnosis due to recurrence after surgery, or spread of cancer to other parts of the body. Most cats with mast cell tumors of the skin will be cured with surgery alone, however up to 20% of cases may later reoccur. With more internal mast cell tumors of liver, intestines, or the spleen, the prognosis is much more guarded in both dogs and cats. This is because of the advanced nature of the disease at time of diagnosis, as well as the spread of cancer to the liver, lymph nodes, lung, intestine, and bone marrow in many pets.


Vet Tip: It is best to take your dog or cat to the veterinarian to have any unusual skin growths or lumps examined as soon as possible. The earlier a tumor is found and treated, the better the prognosis for your pet. - Michael Dym, VMD  

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