Application of a bcr-specific probe in the classification of human leukaemia.

A genomic probe derived from the breakpoint cluster region (bcr) on chromosome 22q11 was used to assess whether Philadelphia (Ph) chromosome positive chronic myelogenous leukaemia patients have unique patterns of bcr rearrangements and whether this pattern is modified as the disease progresses from stable phase to blast crisis. The data indicated that bcr rearrangements are fairly unique to each patient and are not subject to additional modifications during the course of the disease. We have also found bcr rearrangements in acute lymphocytic leukaemia (ALL) patients, usually of the cALL phenotype. For the majority of Ph+ ALL patients, the breakpoint on 22q11 was in bcr. However, we describe a case of Ph+ ALL without bcr rearrangement, indicating heterogeneity of Ph chromosomes in ALL at the molecular level. Contrary to previous reports, a bcr rearrangement was also identified in a childhood cALL.