Chronic myeloid leukemia associated with B-cell chronic lymphocytic leukemia: evidence of two separate clones as shown by combined cell-sorting and fluorescence in situ hybridisation.

The simultaneous occurrence of Philadelphia positive chronic myeloid leukemia (Ph+ CML) and B-cell chronic lymphocytic leukemia (B-CLL) is a rare event which raises the possibility that the two malignant clones derive from a common, or distinct, malignant stem cells. In this study, we used combined CD19-based cell-sorting and fluorescence in situ hybridisation (FISH) to investigate whether or not the BCR-ABL fusion gene was present in the malignant B-cells of a patient who presented a Ph+ CML/B-CLL association. The CD19+ cells lacked the BCR-ABL rearrangement whereas all CD19-cells exhibited the fusion gene. This result demonstrates that B-cell transformation occurred in a Ph-B-cell subset.