Cumulative clinical experience from a decade of use: imatinib as first-line treatment of chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a malignant disease that originates in the bone marrow and is designated by the presence of the Philadelphia (Ph+) chromosome, a translocation between chromosomes 9 and 22. Targeted therapy against CML commenced with the development of small-molecule tyrosine kinase inhibitors (TKIs) exerting their effect against the oncogenic breakpoint cluster region (BCR)-ABL fusion protein. Imatinib emerged as the first successful example of a TKI used for the treatment of chronic-phase CML patients and resulted in significant improvements in response rate and overall survival compared with previous treatments. However, a significant portion of patients failed to respond to the therapy and developed resistance against imatinib. Second-generation TKIs nilotinib and dasatinib were to have higher efficiency in clinical trials in imatinib- resistant or intolerant CML patients compared with imatinib. Identification of novel strategies such as dose escalation, drug combination therapy, and use of novel BCR-ABL inhibitors may eventually overcome resistance against BCR-ABL TKIs. This article reviews the history of CML, including the treatment strategies used prediscovery of TKIs and the preclinical and clinical data obtained after the use of imatinib, and the second-generation TKIs developed for the treatment of CML.