CLINICAL MANIFESTATIONS In most cases CML is a biphasic or triphasic disease. The initial chronic phase may last several years without change, but ultimately it either changes abruptly to an acute phase or, more commonly, evolves slowly into a phase of "acceleration," which later progresses to the acute phase. The acute phase is usually defined by the observation of >30% blasts or blasts plus promyelocytes in the blood or marrow,57 but criteria for defining the accelerated phase are imprecise.58 A reasonable classification has been proposed by the International Bone Marrow Transplant Registry (Table 73-2). Table 73-2. Criteria Established by the International Bone Marrow Transplant Registry for Classifying the Phases of CML 1). Chronic phase No significant symptoms (after treatment); None of the features of accelerated phase or blastic phase. 2). Accelerated phase WBC count difficult to control with conventional use of busulfan or hydroxy- urea in terms of doses required or shortening of intervals between courses Rapid doubling of WBC count t<5 days) =-:10% blasts in blood or marrow 2:20% blasts plus promyelocytes in blood or marrow a:20% basophils plus eosinophils in blood Anemia or thrombocytopenia unresponsive to busulfan or hydroxyurea Persisent thrombocytosis Additional chromosome changes (evolving new clone) Increasing splenomegaly Development of chloromas or myelofibrosis Blastic phase 2:30% blasts plus promyelocytes in the blood or bone marrow (Data from International Bone Marrow Transplant Registry.)