Mast Cell Tumors in Cats
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 mast cell tumors in cats?
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 of mast cell tumors in cats?
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

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),
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.

Does cancer cause pain in pets?
Pain is common in pets with cancer, with some tumors causing more pain than others. In addition to pain caused by the
actual tumors, pets will also experience pain associated with cancer treatments such as surgery, radiation therapy or
chemotherapy. Untreated pain decreases the pet's quality of life, and prolongs recovery from the illness, treatment or injury.
It is, therefore, essential that veterinary teams that are taking care of pets with cancer should also play a vital role in
educating pet owners about recognizing and managing pain in their pets. The best way to manage cancer pain in pets is to
prevent it, a term referred to as preemptive pain management. This strategy anticipates pain ahead of time and administers
pain medication before the pet actually experiences pain, thus ensuring the pet's maximum comfort.

To learn more about which tumors are likely to cause a lot of pain, how to recognize pain in pets with cancer and what
cancer pain management options are available for your pet, please visit the
Cancer Pain Management section.

How important is nutritional support for petswith cancer?
Cancer cachexia (a term referring to progressive severe weight loss) is frequently observed in pets with cancer. Pets with
cancer lose weight partly because of lack of appetite and partly because of cancer-induced altered metabolism. Some of the
causes for decreased appetite are related to the cancer itself (for example, tumors may physically interfere with food
chewing, swallowing, and digestion process) and some may be related to the side effects of cancer treatment (for example,
some chemotherapy drugs cause nausea and vomiting, and radiation therapy can cause mouth inflammation).

Proper nutrition while undergoing cancer treatment is essential to maintain your pet's strength, improve survival times,
quality of life and maximize response to therapy. Adequate nutritional support was shown to decrease the duration of
hospitalization, reduce post-surgery complications and enhance the healing process. Additionally, pets with cancer need to
be fed diets specifically designed to provide maximum benefit and nutritional support for the patient. To learn more, please
visit the
Cancer Nutrition section.

What are the treatment options for cats with mast cell tumors?
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 for cats with mast cell tumors?
Although there are no clinical trials for cats with mast cell tumors, there are several clinical trials available for cats with any
tumor type for which your pet may qualify. To learn more these trials (which are partially or fully funded by the institutions),
please visit the
Cat Clinical Trials (any tumor type) section.  

To learn more about veterinary clinical trials in general, please visit the
Pet Clinical Trials section.

What is the prognosis for cats with mast cell tumors?
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 cats with intestinal MCTs face poor prognosis and die or are euthanized after the diagnosis.

  • 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.
Comprehensive guide to cancer diagnosis and treatment in cats and dogs
© 2007 Pet Cancer Center. ALL RIGHTS RESERVED.
Last updated 2/21/2017