Minimal residual disease in acute myeloid leukemia: coming of age

The achievement of complete hematologic remission (CR) is a prerequisite for cure in acute myeloid leukemia (AML). The conventional definition of CR, based on the morphologic recognition of ≤ 5% of leukemic blasts in the BM, does not provide sufficient insight into the quality of the response. Despite CR rates of 50%-80% (depending on age), the majority of patients with AML relapse within 3-5 years from diagnosis. Therefore, there is great need of more sensitive prognostic factors that can predict relapse. Minimal residual disease (MRD), defined as any measurable disease or leukemia detectable above a certain threshold (defined by the methodology applied), predicts failure to maintain a morphologic CR and affects survival negatively. AML is lagging behind acute lymphoblastic leukemia with respect to the implementation of MRD criteria for guidance during therapy. AML is particularly disadvantaged compared with acute lymphoblastic leukemia in that approximately half of AML patients lack a molecular target suitable for MRD monitoring. The detection of altered antigen (Ag) expression by leukemic myeloblasts is a valid alternative to DNA- or RNA-based MRD assays. Although associated with presenting prognostic factors (eg, cytogenetics and genotype), MRD represents the collective end result of all of the cellular mechanisms that determine a patient's response to a given therapy. Therefore, MRD has 2 potential roles in AML treatment: (1) as a posttherapy prognosticator used to assign patients to optimal postinduction/consolidation therapy, and (2) as an early surrogate end point for the evaluation of therapy efficacy.