Imatinib Mesylate in Treating Patients With Myelofibrosis

PRIMARY OBJECTIVES: I. To determine the response rate (complete and partial) to STI-571 in patients with myelofibrosis. II. To determine the safety of STI-571 in patients with myelofibrosis. SECONDARY OBJECTIVES: I. To determine the effects of STI-571 on bone marrow morphology (including effects on marrow fibrosis, osteosclerosis and cellularity) in patients with myelofibrosis. II. To assess the effects of STI-571 on surrogate biologic endpoints including PDGFR expression (by immunohistochemistry), PDGFR signaling, and circulating progenitor (CD34 positive) cells. III. To determine the effects of STI-571 on bone marrow cytogenetics in patients with an abnormal karyotype. OUTLINE: This is a multicenter study. Patients are stratified according to Dupriez risk score (low vs intermediate vs high). Patients receive oral imatinib mesylate once or twice daily on days 1-28. Courses repeat every 28 days for 12 months in the absence of disease progression or unacceptable toxicity.