The effectiveness of Gleevec in the treatment of CML is of particular importance, since CML is characterized by a gene fusion of breakpoint cluster region and c-Abl (BCR-Abl) that results in a constitutively active kinase and uncontrolled proliferation of hematopoietic stem cells. Here, ABL1 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.