Résumé
Chronic myeloid leukemia (CML) patients treated with imatinib develop frequent resistance generally due to a point mutation. Recently, large rearrangements of abl sequence have also been described. In this study, we focused on the complete deletion of exon 7. We screened for bcr-abl(delexon7) in 63 resistant patients by high-resolution melting (HRM) analysis and direct sequencing. Moreover, we analyzed expression of abl(delexon7) and bcr-abl(delexon7) in 17 CML patients at diagnosis, 32 patients at resistance, and 20 negative controls by quantitative PCR or fragment length analysis. bcr-abl(delexon7) was detected on 34 (54%) among 63 resistant patients by HRM, showing an increase in the sensitivity of screening, because only 3.2% could be detected by direct sequencing. This deletion was not associated with a point mutation (P = 0.3362). In addition, abl(delexon7) was found in all tested samples with the same pattern of expression, suggesting an alternative splicing mechanism. In the bcr-abl component, there was no statistical difference between CML patients at diagnosis and resistant patients (P = 0.2815) as regarding bcr-abl(delexon7) proportion, thus arguing against involvement of deletion in resistance. Moreover, among two patients harboring bcr-abl(delexon7) at diagnosis, one experienced a complete disappearance of this transcript, and the other decreased >75% at resistance. In conclusion, bcr-abl(delexon7) is frequently observed in CML patients when using sensitive techniques. It seems to be the result of an alternative splicing mechanism and to be independent from the occurrence of resistance.