Chronic lymphocytic leukemia in the course of chronic myelocytic leukemia: evidence of independent clonal origin as shown by interphase fluorescence in situ hybridization and fluorescence-activated cell sorting.

We report the case of a 57-year-old man who developed chronic lymphocytic leukemia (CLL) several months after the initial diagnosis of Philadelphia (Ph) chromosome-positive (Ph(+)) chronic myelocytic leukemia. CLL cells were purified by using fluorescence-activated cell sorting and further analyzed using interphase fluorescence in situ hybridization with probes to detect the BCR/ABL fusion gene. We provide evidence that the CLL cells arose in a Ph(-) clone.