Determination of BCR−ABL Overexpression by Correlating qRT−PCR and IP−FISH in Imatinib Treated CML Patients

BIANCHINI M., GARGALLO P., ALÚ F., BENGIÓ R., DE BRASI C., LARRIPA I.

Atlanta (USA)

Congreso; 49th American Society of Hematology; 2007

Imatinib mesylate has proven to be the most effective treatment in chronic myeloid leukemia. Nevertheless, Imatinib resistance has raised concern and prompted interest in additional strategies to achieve disease eradication. Resistance to Imatinib is mainly associated to 3 mechanisms: acquired mutations in the kinase domain of BCR-ABL protein, genetic amplification and transcript overexpression of BCR-ABL rearrangement. Therefore an accurate assessment of resistance mechanism is particularly important to improve strategies to overcome resistance. With the aim to determine overexpression of BCR-ABL, we propose a method that correlates qRT-PCR and FISH data from the same peripheral blood sample. The ratio between both methodologies permits to calculate the Expression Index (EI) for each patient. EI allows estimating the rate of BCR-ABL transcription per rearrangement. The median EI value including all cases was 0.347; those cases included in percentile 90 showed an increment of EI above 1 Log (> 3.478) respect to the median value that we defined as cases with overexpression. We also evaluated the EIs using ROC curve; choosing an EI cutoff of 1.836 we obtained a sensitivity of 95% and a specificity of 61%. By this analysis more patients (n=14) were included in the overexpressing group; patients within this group were resistant to Imatinib though neither kinase point mutations nor gene amplification could be detected. These results show that EI cutoff value is a potential useful marker for BCR-ABL overexpression detection.