Mast Cell Tumors

Mast Cell Tumors (MCT) are the most common malignant (cancerous) tumor in the dog. It is less common in the cat. Mast cells are a normal component of the immune system and are involved in the body’s response to tissue injury. What causes these normal cells to “turn on” and become tumors is not clear. There seems to be a breed predisposition. Boxers, Boston bulldogs, English bulldogs, bull terriers and Siamese cats are diagnosed with MCT more than other breeds. Sites of chronic irritation or inflammation are suspected in some cases and even a virus has been theorized. The bottom line is – we don’t really know why MCT’s form.

Most animals with MCT’s seem to be in perfect health otherwise. Due to chemicals inside mast cells (histamine being the most notable) some animals will have problems with vomiting, ulcers or GI bleeding. In these cases, an antacid such as Famotdine can be helpful. Mast Cell tumors can also develop in the liver, spleen, and lymph nodes leading to other symptoms.

Diagnosis of MCT is based on biopsy results. We can get suspicious we are dealing with a MCT from a fine needle aspirate, but the definitive diagnosis only comes from a biopsy. Some MCT’s are not aggressive or invasive, while others can be very aggressive and invasive. The pathologist will examine the tissue and determine it’s “grade.” There are three grades: I, II, and III. Grade I is the “best,” while grade III is the worst.

Treatment for MCT sometimes requires a second, more radical surgery. There are also several chemotherapy options as well as radiation therapy. It will depend on the pet, the owners and the location of the tumor(s).

Diagnoses of a Mast Cell Tumor can be a frightening thing. It is a very unpredictable form of cancer. Some animals will be cured and others will not. The goal is to maintain a good quality of life for as long as possible