Detection and monitoring of minimal residual disease has become one of the most prevalent topics in CML therapy. The goal of early detection of residual disease is to allow timely therapeutic intervention before overt relapse of disease occurs that has become resistant to therapy. The most powerful tool to serve this purpose is PCR. Major improvements in assay techniques have advanced PCR from a purely qualitative test with considerable variability of test results to an RQ assay with far more reproducible results than were possible before. At the same time, treatment of CML has changed dramatically since the introduction of imatinib. Integration of therapy and molecular assays such as PCR, in addition to a better understanding of the pathophysiology of CML, has assumed even more importance. Quantitative PCR testing has become the standard monitoring strategy for patients undergoing SCT. Although correlations exist between positive test results and probability of relapse, no absolute guidelines for monitoring have been established, especially for patients treated with imatinib. The real impact of the use of RQ-PCR on the validity of predicting relapse according to treatment (SCT, IFN-α, imatinib) will become apparent over time. It is unlikely, however, that any of the results can be fully appreciated without thorough integration of the molecular biology of CML and, as an extension to that, the influence that different therapeutic modalities exert on it.
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