Monitoring of minimal residual disease in leukemia, advantages and pitfalls

The term 'minimal residual disease' (MRD) defines the level of disease detectable in patients in clinical remission during therapy, below the detection limit of conventional methods. Very sensitive methods can be used, able to identify one leukemic cell out of 10,000 normal lymphocytes. In vivo measurements of leukemia cytoreduction reflect the combined effect of clinical and biological variables, thus providing direct information on the effectiveness of treatment in each patient. Thus, these methods can potentially be used for tailoring treatment and personalize the cure. Although MRD studies are becoming an integral part of the modern management of patients with leukemia, several parameters are critical for the application and interpretation of MRD studies, including therapeutic context, timing of sampling, target genes and sensitivity of the polymerase chain reaction (PCR) assay, inter-laboratory standardization (particularly relevant in multicenter studies), selection of patients, retrospective or prospective nature of the study. Methodologies and pitfalls as well as results of clinical uses of MRD will be reviewed in this article by selecting significant examples of its clinical impact in the management of patients with leukemia.