Preclinical and clinical studies have shown that Abl TK inhibition by STI571 was efficient in both p210 Bcr-Abl-positive and p185Bcr-Abl-positive cell lines as well as in primary leukaemia cells obtained from patients having Ph-positive CML and ALL (Beran et al, 1998). This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.