The pathogenesis and clinical patterns of blastic crisis of chronic myeloid leukemia.

Blast crisis terminates the life of the majority (approximately 80%) of patients with CML. The time of its onset appears to be a random phenomenon, varying from a probable coincidence occurrence with the onset of CML to more than a decade after onset of the chronic phase. In most patients the diagnosis is obvious as very immature cells are found to be the predominant cell in blood and marrow. However, in some, the onset is fairly subtle and the diagnosis of the syndrome will be dependent upon ancillary clinical and laboratory clues supplementing morphologic appearance of the blood and bone marrow. The same spectrum of morphological cell types is observed in blast crisis as is observed in acute myeloid leukemia. The predominant cells usually are myeloblasts and promyelocytes but may be immature monocytes, myelomonocytes, proerythroblasts, or immature megakaryocytes. These and other findings imply that the defect resides in the pluripotent hematopoietic stem cell. It is possible, but by no means proven, that lymphoblastic conversion also may occur. Therapy of blast crisis is quite unsatisfactory but clearly is of benefit in some patients.