Imatinib mesylate (IM)/Gleevec/STI571, a rationally-designed agent that occupies the ATP-binding site of BCR-ABL and stabilizes the protein in its inactive conformation, has been a remarkable success for the treatment of chronic myeloid leukemia (CML)[1]–[4]. This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.