DUPLICATION OF CHROMOSOME-9 CARRYING A BCR ABL CHIMERIC GENE IN PHILADELPHIA-CHROMOSOME NEGATIVE CHRONIC MYELOID-LEUKEMIA/

We investigated a patient with Philadelphia chromosome (Ph) negative b ut BCR positive chronic myeloid leukemia (CML) by fluorescence in situ hybridization (FISH). In the chronic phase one chromosome 9 contained a BCR/ABL fusion gene instead of chromosome 22. Although in blast cri sis, both chromosomes 9 had BCR/ABL fusion genes. This could be caused by duplication of the rearranged chromosome 9, which may have a signi ficance similar to a double Ph chromosome. This may suggest that the c ritical event in CML is the formation of a BCR/ABL chimeric gene regar dless of its locus in the genome.