Mast cell tumors in cats.

Mast Cell Tumors in Cats

Dogs

What are mast cell tumors?
Mast cells are present in most tissues, and are especially prominent in the skin, lining of the lungs and digestive tract,
mouth and nose. They are an important component of the immune system, with functions in inflammation and allergy
reactions. Mast cell tumors (MCTs) are formed by the abnormal proliferation of mast cells, and when the entire body is
affected, the disease is referred to as mastocytosis. Mast cells can release several biologically active chemicals such as
histamine and heparin, which can be very damaging to the body when released in excess by the tumor cells.

There are two distinct forms of skin MCTs in cats: 1) the typical mastocytic MCTs that resemble those in dogs and 2) the
less common histiocytic MCTs. The mastocytic MCTs can be further classified into compact and diffuse. The compact
form is estimated to affect 50-90% of the cases and is associated with a more benign (noncancerous) behavior whereas
the diffuse form has a more malignant (cancerous) behavior.

How common are these tumors?
MCTs are the second most common skin tumor in the cat, accounting approximately for 20% of all skin tumors. The
average age of diagnosis for typical MCTs is 10 years and for histiocytic MCTs 2.4 years. Several studies suggest that
Siamese cats may be at higher risk of developing MCTs of both types. MCTs of the internal organs such as spleen or
intestines are more common in cats compared to dogs..

What are the symptoms?
Skin MCTs are usually detected by owners as solitary, raised, firm, hairless lumps on the skin. These lesions are often
white, or less commonly pink. Other forms that have been described include flat, plaque-like lesions. Approximately 20%
of cats with MCTs will have multiple nodules and about 25% will have some ulceration of the masses present. In contrast
to dogs, the head and neck are the most common sites for MCTs in the cat, followed by the trunk, limbs, and other
miscellaneous sites. Tumors located on the head often involve the base of the ear and rarely affect the mouth. Affected
cats are usually otherwise healthy.

Cats with disseminated (scattered) MCTs (e.g. in the spleen or intestine) will often show symptoms such as depression,
anorexia, weight loss, and intermittent vomiting. Intestinal MCTs will also often cause bloody stools and fever. Upon
physical examination, the spleen and intestines may reveal present masses. Additional symptoms may be present due to
the release of granules contained in the mast cells, including gastrointestinal ulceration, uncontrollable hemorrhage
(bleeding), or hard breathing.

How is the diagnosis made?
The diagnostic work up in cats is similar to that for dogs. Mast cell tumors are initially diagnosed by fine-needle aspriation
(FNA) cytology. While FNA is useful, it does not provide any information about the tumor's grade (level of
aggressiveness), and biopsy is therefore recommended. Additional diagnostic steps will vary depending on the tumor's
location, size and initial findings.

For suspected spleen or intestinal MCTs, the veterinarian will typically do a blood test to check for overall health of the
cat, buffy coat smear test to check for circulating mast cell tumor cells throughout the body, bone marrow aspiration to
check for MCT dissemination (spread), coagulation profiler and serum biochemistry profile. One third of cats with this
disease are anemic and up to 50% of cats with spleen MCT will have evidence of bone marrow and buffy coat
involvement. In the case of intestinal MCT, up to 90% of cats will show laboratory evidence of coagulation abnormalities,
which is important to know prior to surgical treatment.

The veterinarian will also examine the regional lymph nodes to check for cancer spread, abdominal ultrasound to check
for metastasis (cancer spread) to the spleen or liver, chest X-rays to check for metastasis to the lungs and fluid
accumulation in the chest, and bone marrow aspiration to check for MCT dissemination (spread). Advanced imaging such
as CT (computed tomography) can be a very useful diagnostic tool that can evaluate the extent of the disease in more
detail and can aid the oncologist to planning an appropriate treatment strategy.

Do these tumors cause pain?
It is imperative that pets with cancer are provided with pain medication to relieve discomfort caused by the disease as well
as by the treatments. To learn more, please visit the Cancer Pain Management section.

What food should be fed to pets with cancer?
Pets with cancer need to be fed diets specifically designed to support a cancer patient. To learn more, please visit the
Cancer Nutrition section.

What are the treatment options?
Surgery is the preferred treatment for the mastocytic form of skin MCT. Most of these masses behave as benign tumors
and can, therefore, be easily excised. The local recurrence of the tumor (growing back) is estimated to occur in 0-24% of
cats after surgery and the spread throughout the body is estimated to affect 0-22% of cats post-surgery. The treatment of
diffuse mastocytic tumors usually requires a more aggressive surgical approach (as described in the dog section) due to
the high potential of this tumor type to recur and metastasize. Histiocytic MCTs in younger cats can be either surgically
removed or the pet owners can adopt the 'wait and see' approach in the case of multiple masses since most are reported
to regress spontaneously. Cats with spleen MCTs are usually treated with surgery and surprisingly, many cats enjoy long-
term survival (12-19 months) even if bone marrow and peripheral blood are involved. Unfortunately, there is not much
information available on the benefit of chemotherapy for the treatment of MCTs.

Are there any clinical trials investigating new treatments?
There are only a few available clinical trials investigating new treatments for mast cell tumors in pets. To learn more about
veterinary clinical trials in general, please visit the Pet Clinical Trials section. To learn more about clinical trials open to
enrollment in the United States, please visit Clinical Trials for Mast Cell Tumors section.

To help Pet Cancer Center conduct more mast cell tumor clinical trials across the United States in order to make novel
and more efficacious therapies available to pets, please

What is the prognosis?
The metastatic rate (spread to distant organs) for MCTs seems to vary considerably, ranging from 0% to 22%. In the
case of spleen or intestinal MCTs, widespread dissemination and metastasis (spread) are much more common. One study
of 30 cats with spleen MCTs showed dissemination to the liver (90%), lymph nodes (73%), bone marrow (40%), lung
(20%) and intestine (17%). Intestinal MCTs commonly metastasize to the liver and less commonly to the spleen, lung, and
bone marrow. Most animals with intestinal MCTs face poor prognosis and die or are euthanized after the diagnosis.

Additional online resources:

Sources:

Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.
Morrison Wallace B. Cancer in Dogs and Cats: Medical and Surgical Management. Baltimore: Williams&Wilkins,
1998.