Abstract
Imatinib is considered standard therapy for patients with chronic myelogenous leukemia (CML), inducing a high rate of hematologic and cytogenetic responses. Despite these excellent results, several patients develop resistance to imatinib. Mechanisms of resistance are varied and include BCR-ABL1 kinase domain mutations, decreased entry of imatinib into cells, acquisition of secondary genetic changes and activation of alternate signaling pathways. Second-generation tyrosine kinase inhibitors (TKI) (dasatinib, nilotinib) were developed as an alternative for patients that develop resistance or are intolerant to imatinib. Dasatinib is a dual Abl/Src kinase TKI that is structurally unrelated to imatinib and is approved for therapy of all phases of CML in patients who are resistant or intolerant to imatinib. Nilotinib is a compound related to imatinib that has greater specificity and improved binding characteristics, and has clinical activity in the setting of imatinib failure. Resistance to multiple TKIs does occur, particularly in patients with the T315I mutation. Several new agents are in development including new TKIs, aurora kinase inhibitors and homoharringtonine.