Chronic myeloid leukemia is a cancer of the white blood cells caused by a fusion of the BCR and ABL genes, which results in uncontrolled proliferation of mature and immature white blood cells. It progresses through three phases - chronic, accelerated, and blast crisis - and is characterized by excessive neutrophils, basophils and eosinophils in the blood and bone marrow. The standard diagnostic tests are detecting the Philadelphia chromosome or BCR-ABL fusion gene via cytogenetic analysis, FISH or PCR. Targeted therapy with tyrosine kinase inhibitors such as imatinib has dramatically improved survival for most CML patients.