Mast Cell Tumor


Mast cells are formed in bone marrow but mature in surrounding tissue. Although mast cells are located in tissue throughout the body, they are mainly found in the skin, respiratory and digestive tracts. They are an important part of the body’s response to inflammation and allergens. Mast cell tumors originate from these mast cells and range from low-grade to high-grade malignancies. With certain tumors there are high local recurrence rates as well as a greater chance the tumors will spread. Once a diagnosis is made, we will perform tests to determine the grade (aggressiveness) and the stage (to what extent the tumor has spread). This will help us determine the best treatment for your pet.

Dogs: Mast cell tumors in dogs are relatively common. They can occur at any age but most cases often develop in middle-age dogs. Some breeds appear to be more susceptible such as Bull Terriers, Boxers and Labrador Retrievers.

Cats: Mast cell tumors are less common in cats than in dogs and are usually diagnosed in cats over 4 years of age. Tumors may develop in the skin, where multiple nodules are most common and tend to be benign. Siamese cats tend to be more susceptible to skin mast cell tumors than other breeds. Internal mast cell tumors originating in the spleen, GI tract or other locations can also develop.

Signs and Symptoms:

Symptoms for both cats and dogs are dependent on the location and aggressiveness of the tumor. Tumors may fluctuate in size or start growing rapidly after months of inactive or subtle growth. Redness and fluid build-up may also be present. Pets may scratch tumors due to higher levels of histamines present. Some tumors may start out resembling a small wart, an allergic reaction or even a bug bite. Lymph nodes near the area of the tumor may be swollen. If tumors have spread, your pet’s liver and spleen may be enlarged. Depending on the stage of the disease, loss of appetite, diarrhea and vomiting may occur.


When you come in for your appointment, we will go through your pet’s medical history including when you first noticed symptoms. This information is important as it may give us insight into which organs may also be affected. The best way for us to test for mast cell tumors is a fine needle aspirate of the tumor. We can test for the presence of abnormal amounts of mast cells in the blood. For a definitive diagnosis and important grading information, we will need to perform a surgical biopsy, which will be useful in determining a specific treatment plan. We may recommend additional tests such as cytology or biopsy of lymph nodes, liver, spleen or bone marrow as well radiographs and ultrasound images to determine the possible extent of disease spread.


Anytime you manipulate a mast cell tumor histamines will be released into the blood stream therefore we tend to prescribe antihistamines to alleviate some of the symptoms prior to any procedure. Surgery is the preferred treatment for mast cell tumors in the skin. Removal of the spleen is recommended for mast cell tumors of the spleen. We may we need to perform cytology or biopsy of lymph nodes or other suspicious internal organs and in some cases surgically remove lymph nodes near the tumor. Follow-up radiation therapy and/or chemotherapy may be beneficial for some pets. We will discuss all options based on your goals and your pet’s evaluation.


Once your pet completes treatment, we will want to monitor for signs of recurrence, spread or the development of any new masses on a regular basis.

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