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The discovery of molecularly targeted agents that selectively inhibit bcr-abl tyrosine kinase activity, such as imatinib, has revolutionized the treatment and natural history of chronic myelogenous leukemia (CML). Treatment of chronic-phase CML with imatinib showed complete cytogenetic response rates of more than 40% in patients after failure of interferon-α, and more than 80% in patients with newly diagnosed CML. Patients with CML can now expect excellent long-term survival, often without major side effects. In most patients, however, residual leukemic burden remains detectable using a sensitive reverse transcription-polymerase chain reaction method. In addition, many patients undergoing imatinib therapy will either not respond or lose their response over time because of resistance or intolerance. The introduction of second-generation tyrosine kinase inhibitors (TKIs) re-establishes response in approximately half of these patients. Several agents are being developed for treating patients who experience suboptimal response to second-generation TKIs and for those who develop resistance caused by the emergence of highly resistant BCR-ABL1 mutations. This article provides an overview of novel targeted agents available for CML.

The advent of imatinib has dramatically improved outcomes in patients with chronic myelogenous leukemia (CML). It has become the standard of care for all patients with newly diagnosed chronic-phase CML based on its successful induction of durable responses in most patients. However, its use is complicated by the development of resistance in some patients. Dose escalation might overcome this resistance if detected early. The second-generation tyrosine kinase inhibitors (TKIs) dasatinib and nilotinib provide effective therapeutic options for managing patients resistant or intolerant to imatinib. Recent studies have shown that dasatinib and nilotinib provide quicker and potentially better responses than standard-dose imatinib when used as a first-line treatment. The goal of therapy for patients with CML is the achievement of a complete cytogenetic response, and eventually a major molecular response, to prevent disease progression to accelerated or blast phase. Selecting the appropriate TKI depends on many factors, including disease phase, primary or secondary resistance to TKI, the agent's side effect profile and its relative effectiveness against BCR-ABL mutations, and the patient's tolerance to therapy. In October 2010, NCCN organized a task force consisting of a panel of experts from NCCN Member Institutions with expertise in the management of patients with CML to discuss these issues. This report provides recommendations regarding the selection of TKI therapy for the management of patients with CML based on the evaluation of available published clinical data and expert opinion among the task force members.

The 2014 NCCN Clinical Practice Guidelines in Oncology for Chronic Myelogenous Leukemia recommend quantitative reverse-transcription polymerase chain reaction (QPCR) standardized to International Scale (IS) as the preferred method for monitoring molecular response to tyrosine kinase inhibitor (TKI) therapy. A BCR-ABL1 transcript level of 10% or less (IS) is now included as the response milestone at 3 and 6 months. Change of therapy to an alternate TKI is recommended for patients with BCR-ABL1 transcript levels greater than 10% (IS) at 3 months after primary treatment with imatinib. Continuing the same dose of TKI or switching to an alternate TKI are options for patients with BCR-ABL1 transcript levels greater than 10% (IS) at 3 months after primary treatment with dasatinib or nilotinib. The guidelines recommend 6-month evaluation with QPCR (IS) for patients with BCR-ABL1 transcript levels greater than 10% at 3 months. Monitoring with QPCR (IS) every 3 months is recommended for all patients, including those who meet response milestones at 3, 6, 12, and 18 months (BCR-ABL1 transcript level ≤10% [IS] at 3 and 6 months, complete cytogenetic response at 12 and 18 months).