Therapy of HES, PV, Atypical Chronic Myelocytic Leukemia (CML) or Chronic Myelomonocytic Leukemia (CMML), and Mastocytosis With Imatinib Mesylate

Imatinib mesylate is a chemical compound that blocks a protein that is responsible for a certain form of leukemia. However, imatinib mesylate also blocks other important proteins that may be responsible for other blood diseases such as myeloproliferative disorders. Patients in this study will take 4 tablets of imatinib mesylate by mouth every day. Patients with HES will take 1 tablet daily to begin, and may go up to 4 tablets daily depending on response. Imatinib mesylate should be taken each morning at breakfast with a large glass of water. Bottles containing the tablets will be given to the patient every month. Unused supplies must be returned at the end of the study. Patients taking oral hydroxyurea to control their blood counts, can continue it during the first month of imatinib mesylate treatment, but must stop taking it from then on. After completing 2 months of therapy, response to imatinib mesylate will be evaluated. If the response is good, treatment with imatinib mesylate alone will be continued. If the response is not good, the dose of imatinib mesylate will be increased to 8 tablets daily (4 in the morning and 4 in the evening) or may be decreased to 3 tablets daily. This will be based on how the drug is tolerated. Treatment may be continued for up to one year, or as long as it is judged best to control the leukemia. Patients will be asked to visit their doctor for a physical exam and vital signs. The frequency of doctor visits will vary depending on physical condition. Blood tests (about 2 teaspoons) will be done once each year. The blood samples will be used for routine lab tests. A bone marrow sample will also be taken to check and measure cells related to the disease after 3 - 4 months, then every 3-6 months in the first year. If the initial bone marrow sample does not show disease, repeated bone marrows will not be done. This is an investigational study. Imatinib mesylate has been approved in CML for patients whose disease has not responded to interferon. However, this is an investigational study in patients with myeloproliferative diseases. The FDA has authorized the use of imatinib mesylate in research. A total of 145 patients will take part in this study. All will be enrolled at MD Anderson.