Minimal residual disease studies in acute leukemia

Studies of minimal, or submicroscopic, residual disease (MRD) during treatment hold great potential for improving the clinical management of patients with acute leukemia. MRD assays can accurately gauge treatment response and allow estimates of the residual leukemic cell burden during clinical remission in individual patients, thereby refining the selection of therapeutic strategies and, possibly, long-term clinical outcome. The most useful MRD assays currently available are polymerase chain reaction amplification of fusion transcripts and rearranged antigen-receptor genes, and flow cytometric detection of aberrant immunophenotypes. Several studies in children and adult patients with acute lymphoblastic leukemia and acute myeloid leukemia have shown a strong association between MRD and risk of relapse, irrespective of the methodology used to detect residual disease. This article discusses the relative merits of the available MRD assays and the significance of MRD in relation to clinical and biologic features of the disease, and treatment outcome.