The goal of this clinical research study is to see if Gleevec, known as imatinib mesylate (STI571), can improve the disease condition in patients with hypereosinophilic syndrome, polycythemia vera, atypical CML or CMML with PDGF-R fusion genes, or mastocytosis.

Optional Procedures: Patients will be asked to have some extra blood and/or bone marrow samples taken. These samples will be used to evaluate the effect of the treatment on leukemic cells.

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.

Before treatment starts, patients will have a physical exam, including medical history and documentation of disease, blood tests, and a bone marrow study. The bone marrow will be removed with a large needle. Women able to have children will have a screening blood or urine test for pregnancy.

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. Continued monitoring of blood tests will be required every week during the first month then every 2 to 4 weeks from then on.

Blood tests (about 2 teaspoons) will be done every 2-6 weeks for the first 6 months on study, then every 3-4 months. 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 M. D. Anderson.

Optional Procedures: Patients who agree will have about 2 teaspoons of blood and/or bone marrow taken before therapy and every 3 months during therapy. To collect a bone marrow biopsy, an area of the hip or chest bone is numbed with anesthetic and a small amount of bone marrow is withdrawn through a needle.

You do not have to agree to take part in the optional procedures in order to receive treatment on this study.

• Chronic Myelomonocytic Leukemia
• Chronic Myeloid Leukemia
• Polycythemia Vera
• Hypereosinophilic Syndrome
• Mastocytosis

Inclusion Criteria:

1. Patients must have 1 of the following hematopoietic malignancies: Hypereosinophilic syndrome (HES), Polycythemia vera (PV), Atypical CML or CMML with PDGF-R fusion genes, Mastocytosis, Serum bilirubin less than 2 mg%, serum creatinine less than 2 mg% unless abnormality is considered due to hematologic malignancy by investigator, ECOG performance status < 3, life expectancy > 12 weeks
2. Patients must sign informed consent indicating they are aware of the investigational nature of the study, in keeping with policies of the hospital, women of pregnancy potential must practice birth control. Women and men must continue birth control for the duration of the trial and at least 3 months after the last dose of study drug. Inclusion of women and minorities: As per NIH policy, women and members of minorities will be included in this protocol as they are referred in the relevant populations.
3. There are no exclusions of women or minorities based on the study objectives, NYHA Class <3.

Exclusion Criteria: None