BCR ABL FUSION LOCATED ON CHROMOSOME-9 IN CHRONIC MYELOID-LEUKEMIA WITH A MASKED PH CHROMOSOME/

A reciprocal translocation, t(10;22)(q22;q11), resulting in a masked P h chromosome was identified in a patient diagnosed with chronic myeloi d leukemia (CML). Both homologs of chromosome 9 were of the normal pat tern. Two signals for the ABL probe, both of them hybridized to chromo some 9, were demonstrated via fluorescence in situ hybridization (FISH ). Furthermore, cohybridization with two differently labeled BCR/ABL t ranslocation DNA probes indicated a BGR/ABL fusion apparently located on 9q34. Molecular studies revealed a rearrangement of the BCR region and expression of a chimeric BCR/ABL mRNA of CML configuration. These findings indicate that the BCR/ABL fusion resulted from an unusual rel ocation of the BCR gene from its normal position on 22911 to 9q34 adja cent to the ABL gene.