Dr. Kim Freeman, DACVIM Oncology

As previously discussed, mast cell tumors (MCTs) can occur on the skin and can also be found in the liver and spleen of cats. The prognosis and behavior of a mast cell tumor is different, depending on where the tumor is found. However, a mast cell is still a mast cell, regardless of the location.

What does this mean? A normal mast cell is a white blood cell that is part of the allergy system. It makes a variety of substances that can trigger allergic reactions. Histamine is the primary substance made by mast cells. It’s the stuff that causes the red, itchy skin and hives seen with allergies. It can also cause stomach ulcers, vomiting, diarrhea, low blood pressure and anaphylaxis in severe allergic reactions. So, when we deal with mast cell cancer, we must always remember that cancerous mast cells can release histamine and cause red, itchy skin, hives, stomach ulcers, vomiting, diarrhea, low blood pressure and anaphylaxis, regardless of where the cancer is growing.

I have talked about mast cell tumors in the skin and in the spleen, but cats can get mast cell tumors in their intestinal tract, as well. The symptoms can be quite similar to all kinds of intestinal problems that are both cancerous or non-cancerous. Some early symptoms may include decreased or loss of appetite, weight loss, depression or lethargy. Other signs include vomiting, diarrhea, or a rounded, full looking belly.

How is mast cell cancer in the intestines diagnosed? A physical exam by a veterinarian is a good starting place. They may notice that your cat’s gums are pale or your cat feels skinny. They may determine your cat has lost weight, by comparing to a previous exam weight. Your vet may feel a mass in the abdomen, suggesting that further testing should be done. Blood work can be helpful in looking for signs of systemic disease. Although blood work is often normal, some cats can have increased numbers of mast cells in their blood (mastocythemia), which can be helpful in making a diagnosis and monitoring response to therapy. An abdominal ultrasound would be the next step in making a diagnosis. If enlarged lymph nodes or an intestinal mass are found, then a fine needle aspirate for cytology should be done to get a diagnosis.

What are the treatment options? Once you have a diagnosis, then going to see a veterinary oncologist is recommended. They can help best determine the plan of action for your loved one. If there is a single intestinal mass, then surgery to remove this mass may be the best option. If there are multiple masses, then surgery may not be the right choice for your cat. Chemotherapy may be discussed, if there is evidence of spread to other organs or lymph nodes.

What is the prognosis? This question is somewhat difficult to answer, based on the limited amount of published information on intestinal mast cell tumors in cats. It has been reported that the survival time after surgery to remove a single intestinal mast cell tumor is only about 4 to 6 months. However, I have seen many cats go on to live one or more years following surgery for this cancer. For this reason, I would not give up hope! I think the literature is very misleading and that our feline patients can have a much better outcome with surgical intervention and possibly the addition of chemotherapy after surgery.