Assessing minimal residual disease in chronic lymphocytic leukemia.

New treatment approaches have substantially improved response rates in chronic lymphocytic leukemia. Accurate assessment of effective combination chemoimmunotherapy requires more sensitive measures of response, and a variety of techniques to measure minimal residual disease (MRD) have been developed. Because many studies demonstrate that MRD eradication is associated with prolonged treatment-free survival, detection of MRD is becoming a standard component of clinical trials. Quantitative approaches using polymerase chain reaction or multiparameter flow cytometry are preferable because they allow comparison of efficacy between different studies. In most clinical settings, the levels of chronic lymphocytic leukemia always increase from the first detection of MRD; the exception is allogeneic transplantation, in which there may be stable MRD levels or delayed MRD eradication. MRD analysis in the peripheral blood also may be used during therapy to predict eventual response and potentially to guide therapy to achieve the optimal outcome.