Chronic myeloid leukemia (CML) is a clonal hematopoietic stem cell disorder 
characterized by Philadelphia chromosome and resultant production of the 
constitutively activated BCR-ABL tyrosine kinase. Imatinib (STI571), selective 
inhibitor of the ABL-tyrosine kinase, inhibits the activity of BCR-ABL tyrosine 
kinase. A phase I and II study of STI571 showed remarkable cytogenetic effect in 
patients with interferon-refractory CML, offering new hope for therapy for CML. 
It will, however, require long-term follow-up data from phase II and III 
clinical studies to validate the effect of STI571 on survival. As therapy for 
CML improves, monitoring minimal residual disease will be important.