Advances in the detection of minimal residual disease

The study of minimal residual disease (MRD) is an attempt to detect and define the significance of leukemia invisible to normal morphologic examination. In many circumstances the clinical significance of MRD detection is unclear, because the technical ability to detect and quantify it has outpaced studies demonstrating its clinical significance. The detection of minimal residual disease most consistently has been associated with relapse in acute lymphoblastic leukemia, t(15;17) acute myeloid leukemia, and chronic myeloid leukemia post-transplant, especially after T-cell depletion. But, in many types of leukemia, including acute myeloid leukemia and acute lymphoblastic leukemia, MRD can be detected in long-term remission patients without subsequent relapse. The study of MRD is evolving from detecting residual disease and predicting relapse to the study of the mechanisms that explain how minimum residual disease can coexist in a "cured" patient.