PROGNOSTIC-SIGNIFICANCE OF BCR-ABL REARRANGEMENT IN CHRONIC MYELOID-LEUKEMIA

Chronic myeloid leukemia (CML) is a myeloproliferative disorder charac terized by the presence of a reciprocal translocation between chromoso mes 9 and 22 in at least 95% of cases. At the molecular level, this tr anslocation results in the activation of the ABL oncogene of chromosom e 9, which becomes contiguous with the 5' end of the BCR gene on chrom osome 22. The breakpoint usually occurs between exons 2 and 3 (b2-a2 r earrangement), or 3 and 4 (b3-a2 rearrangement) of the major breakpoin t cluster region (M-BCR) of the BCR gene. The aim of the present study was to characterize the type of BCR-ABL transcript in 32 patients wit h CML using the reverse transcriptase-polymerase chain reaction (RT-PC R) and to determine if this type of rearrangement is related to the su rvival of the patients. Our results confirmed that RT-PCR is more sens itive than cytogenetic analysis for identifying the Philadelphia (Ph1) chromosome (96.9% vs 79.3%). The frequencies of b2-a2 and b3-a2 rearr angements were 28.1% and 65.7%, respectively. The survival of patients presenting the b2-a2 or the b3-a2 rearrangement was not significantly different (P = 0.27750). The data suggest that the type of transcript has no prognostic value for CML patients.