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Beaver Lake Animal Hospital
26325 SE 39th Street
Issaquah, WA 98029

Beaver Lake Animal Hospital

26325 SE 39th Street
Issaquah, WA 98029



Mast Cell Tumors

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Mast-Cell Tumors


            Mast-cell tumors occur in dogs and cats.    Their cause is unknown, but 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.  Cats may also develop mast-cell tumors, Siamese cats having the highest frequency.  Once a pet has had a mast cell tumor, any other tumor is suspicious of being one also.

            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.  They can also develop in the spleen and intestine. Malignant mast-cell tumors in dogs are frequently located between the toes.  The appearance of mast cell tumors is variable.  They also can stay as only a localized tumor, or can spread aggressively into surrounding tissues or can become systemic, causing a mastocytosis'.  Up to 20 to 25 % of all skin and subcutaneous tumors in dogs are mast cell tumors.  Mast cell tumors are the 4th ranked tumor in cats.

            The cells of this tumor can produce and release histamine and other substances that affect blood vessels.  Histamines allow blood vessels to be leaky' and allow fluid and red blood cells out of the vessels and into the surrounding tissues.  The result is edema, or swelling and erythema or redness to develop.  Histamine can also lead to gastric ulceration.  Mast cells also can produce heparin which when released interferes with blood clotting.  If a mast cell tumor is bumped or disturbed, it can release its factors and cause any of the above events to occur.  This may be just local, whereas the lump seems to grow many times its original size, or can be systemic. 

            A mast cell tumor may be diagnosed by a fine needle aspirate prior to surgery.  If diagnosed this way, a wide margin, about one inch around the mass is recommended to be removed during excision.  If the whole mass has been excised without prior fine needle aspirate, the pathologist will try to determine how close to the excisional edge the tumor cells are.  Many times, if diagnosed this way, a second more aggressive surgery is recommended with much wider area of tissue removed. 

          Biopsy allows for  grading of tumors from I to III.  Grade 1 may be or is as close to benign as a MCT can be and has improved prognosis over grade 2 or 3.  A tumor that is grade 1 or 2 may over time change to a higher grade tumor.  Grade III is the most aggressive, which has a poor prognosis.  If mast cell tumor of II or III is diagnosed, the extent of disease can be staged by completing chest radiographs (X-rays), ultrasound of the spleen, bone marrow aspirates and lymph node biopsy.  Staging allows better predicting your pet's prognosis, and developing treatment plans.


Important Points in Treatment

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

2.       If diagnosed on surgical biopsy, a second, more aggressive surgical excision is usually recommended.

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

4.       Over-the-counter Pepcid AC 10 mg may be given every 12 hours will help prevent gastric ulceration.

5.       Medicines (antihistamines) may be prescribed to help reduce the affects of histamine.

6.       Surgical patients:

Check the incision site at least once daily.

Report any abnormalities to the doctor.

Restrict your pet's activity until authorized by your doctor.

Prevent your pet from licking or chewing at the incision.

Please call the doctor if licking or chewing is a problem.

Your pet will be evaluated for suture removal in   10  to 20 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.


Click here for a link to a more in depth article on MCTs in Veterinary Partner