Dr. Kim Freeman, DACVIM Oncology

In part I of this blog, we talked about mast cell tumors of the skin in cats. In this post, we will discuss how the same type of cells, called mast cells, can cause cancer in the liver and spleen. You might ask, how does the same kind of cell cause cancer in another part of the body?

Mast cell cancer seems to have different behaviors depending on what part of the body it starts to grow. Typically, mast cell tumors in the skin are benign. If cancerous mast cells are found in internal organs then they are most often malignant. Mast cell cancer in the spleen usually occurs in older cats.

As we discussed in the first blog post on mast cell cancer, mast cells can release histamine and other inflammatory compounds which can lead to stomach or intestinal ulceration, internal bleeding, low blood pressure, labored breathing, and in extreme cases, shock and death. If there is mast cell cancer affecting the spleen, or other internal organs, often some or multiple of these symptoms are present. The severity varies from patient to patient. If your cat were to develop this disease, these are the things you might notice:

  • lethargy or tiredness
  • vomiting
  • loss of appetite
  • weight loss
  • big, full belly – sometimes it can feel soft and wobbly or more firm and full.
  • increased breathing rate

A bloated or distended belly may be a sign that the spleen is enlarged or that fluid is accumulating in the abdomen. If your cat has an increase in breathing rate, it could mean that there’s fluid in the chest cavity. As you can imagine, any of these symptoms mean your cat isn’t feeling too well and you’d better get her into see the vet as soon as possible.

Common tests for MCTs in the spleen
When conducting a physical exam, your vet might be looking for an enlarged liver and spleen, an abdominal mass, pale gums, or decreased lung sounds. The physical exam tells the vet that she needs to order tests to figure out what is causing these changes. Your vet is likely to recommend full blood work, abdominal ultrasound, chest x-rays, and cytology of the spleen or other abnormalities found on ultrasound to look for evidence of spread of the disease. These will help with staging. There is a blood test called a ‘buffy coat analysis’ that will test for mast cells in the blood. This simple test can be useful in monitoring response to treatment

Prognosis for cats who have had a splenectomy
If there is mast cell cancer in the spleen, we generally recommend surgery to remove the spleen (splenectomy). The prognosis even in the face of significant bone marrow, liver, lymph node and peripheral blood involvement can still be good. The long-term survival with a good quality of life is an average of 12-19 months. We have found that removing the spleen makes patients feel a lot better, even if they have disease in other organs.

We are also starting to use chemotherapy in patients to further maintain good quality of life and to improve their survival outcomes. Even though there is not much published about the success of chemotherapy, in practice, we are seeing significant improvements!

Stay tuned for blog part III: intestinal mast cell tumors in cats.