To determine the effect of a highly selective JAK2 inhibitor (BMS-911543) [35] alone or in combination with IM on CML cells, we examined changes in the phosphorylation of STAT5, which is activated by JAK2 kinase and can be used as a measure of JAK2 kinase activity. This evidence concerns the gene JAK2 and chronic myelogenous leukemia, BCR-ABL1 positive.