The tyrosine kinase inhibitor imatinib mesylate (Gleevec) (formerly STI571) has proven to be an effective and safe new therapy for patients with chronic myeloid leukemia (CML). It has induced short-term hematologic control in many patients with advanced-phase CML, with some patients achieving durable responses. In chronic-phase patients it induces significantly better cytogenetic responses and lower progression rates than interferon-alpha. However, relapse is a significant problem, especially for advanced-phase patients, and imatinib alone appears unlikely to be curative in any patient group. Real-time quantitative polymerase chain reaction (Q-PCR) provides an accurate, sensitive, and noninvasive measure of residual leukemia in patients on imatinib. Levels of BCR-ABL in the blood correlate strongly with the bone marrow cytogenetic results and early measurement can predict subsequent cytogenetic response. Complete molecular responses (no BCR-ABL detected by real-time Q-PCR) are rarely achieved. Sequential real-time Q-PCR studies should facilitate rational patient management and allow comparison of different imatinib-based treatment strategies. It may be possible to define levels of molecular response that predict long-term disease control. In addition, by defining patterns of response, an early indication of imatinib resistance may be detected.
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