INFLUENCE OF M-BCR BREAKPOINT SITES ON THE DURATION OF CHRONIC PHASE IN 100 PATIENTS WITH CHRONIC MYELOCYTIC-LEUKEMIA

Rearrangements of the bcr (M-BCR) gene were studied in 100 patients wi th chronic myelocytic leukemia (CML). To determine the significance of a chimeric gene expression in the progression of CML, we analyzed 43 patients for bcr-ABL chimeric mRNA expression. Both DNA and RNA analys es revealed a possible influence of breakpoint sites in the bcr region on the duration of the chronic phase. Patients with the breakpoint lo cated at about the 1-kb region between BamHI and HindIII in bcr exon 3 (region C2) had a significantly shorter chronic phase (31 months) (p = 0.028) than patients in whom the breakpoint was located in other reg ions. When the bcr locus was divided into 5' and 3' regions as for the BamHI cleavage site located near the 5' region of bcr exon 3, the chr onic phase duration in patients with the 5' site (HindIIl-BamHI) and 3 ' site (BamHI-EcoRI site) was 75 and 38 months, respectively. However, the difference was not statistically significant (p = 0.128). These r esults suggest that only the breakpoint site at C2 on the bcr locus, r ather than breakpoint sites in other regions, has an important role in the progression of CML.