Insertion of the 5 ' part of BCR within the ABL gene at 9q34 in a Philadelphia-negative chronic myeloid leukemia

We report a chronic myeloid leukemia patient without evidence of a Philadel phia (Ph) chromosome in whom RT-PCR analysis performed in blast crisis demo nstrated the existence of both common b3a2 and b2a2 BCR/ABL fusion transcri pts. In situ hybridization studies with BCR- and ABL-specific probes showed location of the BCR/ABL fusion gene on chromosome 9, band q34, instead of at chromosome 22q11 and that it resulted from an insertion of the 5' side o f BCR within the ABL gene on chromosome 9. The vast majority of cells showe d a BCR/ABL fusion gene on both chromosomes 9, which is equivalent to a dou ble Ph chromosome, thus reinforcing the notion that the critical event in C ML is the formation of a functional BCR/ABL fusion gene. (C) Elsevier Scien ce Inc., 1999. All rights reserved.