The critical role of the BCR-ABL kinase in CML has been demonstrated by the clinical efficacy of a small molecule inhibitor imatinib mesylate (STI-571, the active ingredient in GleevecTM), that binds to the ABL kinase domain [11], [12], [13], [14]. This evidence concerns the gene BCR and chronic myelogenous leukemia, BCR-ABL1 positive.