Mast cell tumors, or mastocytoma, originate from mast cells, which are ordinarily found in bone marrow and tissue. Mast cell tumors are one of the most common forms of skin cell tumors -- about one-fourth of all skin cell tumors are mast cell tumors. These tumors aren’t always malignant, but they do have the potential to be. Some breeds are more likely to get mast cell tumors than others, including Siamese cats, Bulldogs, Terriers, Retrievers, and German Shorthair Pointers. Older pets also have increased chances of developing mast cell tumors.
But aside from the increased chances with some breeds, the incidence of this form of cancer remains unpredictable, and there is no known preventative method that can be used to ward off these tumors.
Types of Tumors:
Mast cell tumors are divided up into three different grades, and determining which grade of tumor your pet has helps your vet to determine the next best steps in terms of treatment and prognosis. The three grades are:
Grade I: Low grade tumors have cells that are well-differentiated (or resemble regular non-cancerous cells) and are unlikely to metastasize and spread throughout the pet’s body.
Grade II: This middle grade is somewhat differentiated, but not entirely, and has a heightened possibility of metastasis or spreading in the area where the tumor is located.
Grade III: Finally, Grade III tumors are poorly differentiated, and do not resemble ordinary cells. These cells are aggressive and likely to spread throughout a pet’s body.
Both dogs and cats get the same types of mast cell tumors. Additionally, cats can get another, more rare form of the tumors, known as histiocytic.
Pets may have digestion related symptoms, such as a reduced appetite, vomiting, or feces that are a dark black color. But an even more likely sign of these skin tumors are raised skin masses on the skin or subcutaneous layer of your pet; the masses can be either white or pink in color. The mast cell tumors can occur on your pet’s body or limbs -- in later phases, cancerous cells can metastasize and an enlarged liver or spleen is common.
As with most diseases, your vet’s first step will be a thorough physical and medical history of your pet. Fine needle aspiration can be used to remove and examine the cells under a microscope. A biopsy, in which cells are removed surgically from your pet, will allow the veterinarian to determine the grade of the tumor, as well as the stage of your pet’s cancer, if the tumor is cancerous. Sonograms and x-rays can help determine if the tumor has spread or if organs have become enlarged, and a full blood count can identify any secondary symptoms that you pet may have as a result of a cancerous tumor.
Treatment will depend on the grade and placement of the mast cell tumor, but in general, surgery to remove the tumor is the first step. Affected lymph nodes in the area of the tumor may also need to be removed. If the tumor is in a location where surgery isn’t an option, because the mast cell tumor is not easily accessible, then radiation is a possible treatment option. Chemotherapy may also be called for, especially for pets with high grade tumors.
During recovery from surgery, you’ll need to make sure that your pet rests and does not exercise or engage in extreme activity. As well, it’s important that pets do not lick, bite, or gnaw at the site of the surgery, and you should keep an eye on the cleanliness and condition of the site of the surgery. Post-surgery, pets will need to be monitored for reappearance of tumors, and for signs that the tumor had metastasized prior to surgery.
This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.
More on Types of Cancer
Summary of Cancer in Pets
Bone Cancer in Pets
Lymphoma in Cats and Dogs
Histiocytosis in Pets