Accelerated Phase of CML

The accelerated phase of CML may occur at any time during the natural history of this disease, although this phenomenon generally is seen within 30 to 36 months after the initial diagno sis.12,32 This phase, which develops in about one-half of patients, may be heralded by progressive splenomegaly and leukostasis, and a demonstration that the patient has become refractory to previously effective chemotherapy.87 The peripheral blood may show erythroid abnormalities such as marked aniso- and poikilocytosis with circulating myeloblasts and a leukoerythroblastic blood picture. Basophils and eosinophils may increase and thrombocytosis may worsen. A bone marrow biopsy performed at this time is likely to show myelofibrosis; cytogenetic studies may reveal chromosomal abnormalities such as new clonal abnormalities and aneuploidy.88 Features that have suggested entry into an accelerated phase (associated with a median survival of less than 18 months) have included peripheral blood or bone marrow blasts exceeding 15 percent of the nucleated differential, blasts and promyelocytes greater than 30 percent of the differential, or basophils greater than 20 percent of the differential; platelets less than 100 X 109/L; unexplained decrease in hemoglobin (less than 7 g/dl); and extramedullary disease.88

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