Visceral Mast Cell Tumor in Cats

Last Modified: September 17, 2006

Dear OncoLink "Ask The Experts,"

My cat was diagnosed with a mast cell tumor in his abdomen and prescribed cyproheptadine twice a day. I would like to know how this drug works against this disease.

Lili Duda, VMD, Section Editor of the OncoLink Veterinary Oncology Menu, responds:

Mast cells are white blood cells that play a role in allergic reactions, and are responsible for symptoms such as hives, redness/itchiness, and anaphylactic shock. Visceral mast cell tumor, or "mastocytoma", refers to a mast cell tumor that arises within the abdomen. Typically this means the spleen and/or intestines. The mast cell tumor may also be diffusely spread to other sites, such as the liver, lymph nodes, bone marrow, and skin.

Cats with visceral mastocytoma are usually ill, with signs such as lethargy, loss of appetite, vomiting, and diarrhea. Many of the symptoms associated with mastocytoma are due to chemicals contained within mast cell granules, such as histamine. In the cat, histamine can cause allergic type symptoms, such as low blood pressure and difficulty breathing. In addition, histamine triggers stomach acid production which can lead to ulcers.

For cats with mast cell tumor of the spleen that are stable enough to tolerate surgery, removal of the spleen can result in significant improvement, even in cats that have involvement of the bone marrow. There is no known effective treatment for intestinal mast cell tumor, and this condition carries a poor prognosis, so treatment measures are aimed at supportive care. This typically includes antihistamine-type drugs that work on the two types of histamine receptors, H1 and H2. Drugs that block the H1 receptor include diphenhydramine (Benadryl), chlorpheniramine (Chlor-Trimeton), and other similar drugs. Drugs that block H2 receptor include cimetidine (Tagamet), famotidine (Pepcid), and other similar drugs. Cyproheptadine is an H1 antihistamine drug that is most commonly used as an appetite stimulant in cats, but can also be used to treat mast cell tumor.