2. Patients > = 18 years with myelofibrosis (either primary (myelofibrosis with myeloid metaplasia, agnogenic myeloid metaplasia), post polycythemia vera or post essential thrombocytosis) who 1) meet the Mayo Clinic criteria for high risk disease (> = 2 of the following criteria: hemoglobin <10 g/dL, WBC <4 or >30 x 109/L, platelets < 100 x 109/L, absolute monocyte count > = 1 x 109/L) AND 2) have failed to respond to treatment with at least one prior therapy for myelofibrosis (erythropoietic cytokines, androgens, hydrea, interferon, thalidomide, lenalidomide or investigational therapy).