A Study of Gleevec in Patients With Idiopathic Myelofibrosis or Chronic Myelomonocytic Leukemia (CMML)

Inclusion Criteria: * Patients must have a clinical diagnosis of myelofibrosis with myeloid metaplasia or chronic myelomonocytic leukemia (CMML). Patients may be entered based on a prior cytogenetic karyotype showing the absence of the Philadelphia chromosome. * Patients may be entered prior to completion of reverse transcription-polymerase chain reaction (RT-PCR) or fluorescent in situ hybridization (FISH) studies, but a patient who is subsequently found to be BCR-ABL or FISH positive will be removed from protocol treatment. FISH will only be performed on patients with a normal karyotype. A PCR sample will be sent on all patients. * The patients with myelodysplasia must have French-American-British (FAB) subtype chronic myelomonocytic leukemia (CMML) defined as peripheral blood monocytosis, and less than 30 percent blasts in the peripheral blood or the bone marrow. * The patients with myelofibrosis with myeloid metaplasia can have one of the following: agnogenic myeloid metaplasia (idiopathic myelofibrosis), or post-polycythemic myeloid metaplasia (post-polycythemic myelofibrosis), or post-thrombocythemic myeloid metaplasia. * Estimated life expectancy of 6 months or greater. * Serum bilirubin equal to or less than twice the upper limit of normal. * Serum SGOT and SGPT equal to or less than twice the upper limit of normal. * Serum creatinine equal to or less than twice the upper limit of normal. * Age at least 18 years. * Greater than 4 weeks from any chemotherapy (except hydroxyurea), radiotherapy, immunotherapy, or systemic glucocorticoid therapy (non-glucocorticoid hormonal therapy is allowed). Systemic glucocorticoid therapy for non-malignant disease is allowed. * The last dose of hydroxyurea must be 24 hours prior to the initiation of Gleevec. * Greater than 2 months following bone marrow or peripheral blood stem cell transplantation or treatment with donor lymphocyte infusion (DLI). Exclusion Criteria: * Uncontrolled active infection. * Pregnancy or nursing mothers. * Patients with myelofibrosis with myeloid metaplasia or chronic myelomonocytic leukemia who have transformed to acute myelogenous leukemia. * Prior treatment or diagnosis of acute myelogenous leukemia. * Patients with Philadelphia positive cytogenetics by either peripheral blood or bone marrow sampling. * Eastern Cooperative Oncology Group (ECOG) performance status \> 3. * Prior exposure to Gleevec. * Active central nervous system (CNS) disease. * Evidence of infection with the human immunodeficiency virus. * Active psychiatric or mental illness making informed consent or careful clinical follow-up unlikely.