Different kinetic pattern of chronic myeloid leukemia: lymphoblastic and myeloblastic blastic crisis.

Cell kinetic studies were performed in 8 case of lymphoid blastic crisis (BC) of chronic myeloid leukemia at the onset of BC and during subsequent relapses. The results were compared with those found in 7 myeloblastic BC. While in the myeloblastic transformation the labeling index (LI) was always higher in bone marrow than in peripheral blood blasts, suggesting a predominant bone marrow proliferation of the leukemic cells, in the lymphoid transformation a higher LI was often found in peripheral blasts. Moreover, the lymphoblastic transformations were frequently characterized by lymphadenopathy. These findings point to the similarities between lymphoid BC and acute lymphoblastic leukemia, suggesting the possibility that a blastic event may originate in an extramedullary site and that an extramedullary BC is more likely to be lymphoid in nature.