Mastocytosis

Kristi S. Lively, DVM, DABVP

BASIC INFORMATION be done on accessible masses. Chest x-rays may be recommended Description to look for metastasis (spread of the cancer). Mast cells usually reside in connective tissues but are occasion- If bone marrow involvement is suspected, bone marrow aspi- ally found in the bloodstream. They contain granules that store ration may be performed to evaluate the degree of proliferation histamine and other chemicals that activate inflammation. Mast of mast cells. Any masses that are surgically removed are usually cell tumors (MCT) represent the most common form of mast cell submitted for histopathologic examination to determine the degree disease. These tumors usually arise in the skin and are sometimes of malignancy, which can help predict future tumor behavior and called cutaneous mastocytosis. (See the handouts on Mast Cell prognosis. Other tests may be recommended to rule out diseases Tumors in Dogs and Mast Cell Tumors in Cats .) that cause similar clinical signs. Mastocythemia is the presence of abnormal numbers of mast cells in the blood or bone marrow. Mastocythemia may indicate TREATMENT AND FOLLOW-UP a form of disseminated mast cell cancer called systemic masto- Treatment Options cytosis. Although cutaneous MCT is more common in dogs, cats develop systemic mastocytosis more often. Mast cell leukemia Aggressive treatment is recommended whenever mast cell disease develops when malignant mast cells proliferate in the bone mar- is diagnosed. Whenever possible, surgical excision (removal) of row and are released into the circulation (bloodstream). the MCT is performed, followed by appropriate medical or radi- Causes ation therapy. If the spleen is involved, surgical removal of the Mast cells are normally produced in the bone marrow; from there, spleen is indicated. they circulate to other areas of the body. Why mast cells become For animals with systemic mastocytosis, especially in the gut malignant is unknown. A genetic predisposition or viral influ- or in multiple organs, about 50% respond to high doses of predni- ence is suspected for MCT in dogs, but the cause of mastocytosis sone (steroid) for several months, followed by lower doses for 1 remains a mystery in cats. Cancerous mast cells may multiple in year. If no response is detected to steroids after the first 2-3 weeks, the spleen, skin, gut, liver, and other soft tissues. or for highly malignant cells, other chemotherapeutic agents may be considered. L-Asparaginase and vincristine may be recom- Clinical Signs mended in dogs, and lomustine and vinblastine in cats. Supportive Clinical signs depend on the organ system involved. Mast cells care with antacids and gut-protective agents may be used to pre- secrete histamine, a chemical that can cause stomach ulcers. vent stomach ulcers. Antihistamines may also be recommended. Patients with systemic disease may exhibit vomiting, diarrhea, weight loss, and lack of appetite. Heparin may be released by mast Follow-up Care cells and can cause bleeding tendencies, such as abnormal bruising Laboratory tests and sometimes bone marrow aspirations are used or blood in the feces. If the spleen is involved, abdominal disten- to monitor the response to therapy and side effects of the medica- tion or a palpably enlarged spleen may be detected. Acute collapse tions. Tests may also be repeated with any evidence of recurrence may occur following a sudden release of histamine, perforation of of mast cell disease, such as new skin nodules, enlargement of the a gastrointestinal ulcer, or bleeding from the spleen. Patients with liver or spleen, or return of clinical signs. liver involvement may be jaundiced. Prognosis Prognosis varies depending on the response to treatment and the Diagnostic Tests organ systems involved. Patients with rapidly progressive disease Laboratory tests are usually recommended in patients with sus- have a poorer prognosis than patients with slow-growing tumors. pected mast cell disease. The complete blood count may reveal mast Involvement of the liver and gut carries a more guarded prognosis cells in the blood, as well as anemia and alterations in the white than other forms. If the disease does not respond to steroids, prog- blood cell count. Blood clotting tests may be indicated if any abnor- nosis is also poor. mal bleeding or bruising is present. Affected cats may be tested for Cats with splenic mastocytosis often have a good prognosis feline leukemia virus and feline immunodeficiency virus infection. following splenectomy and may live for a few years. Even cats Abdominal x-rays and an ultrasound are often performed to evalu- with mast cell disease in the liver and nearby lymph nodes often ate the spleen, liver, and other organs. Fine-needle aspiration may do well for up to 14 months following splenectomy.