It has been reported that in a proportion of CML BC-derived cell lines, grown in vitro in the continuous presence of imatinib, BCR-ABL gene amplification is observed (Le Coutre et al, 2000; Mahon et al, 2000; Weisberg and Griffin, 2000). This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.