Minimal residual disease in multiple myeloma: bringing the bench to the bedside.

Outcomes for patients with multiple myeloma (MM) have improved substantially in the past decade, with improvements in both progression-free survival and overall survival. Many patients are now achieving a complete response to treatment, and consequently highly sensitive assays are needed for detection of minimal residual disease (MRD) in patients with MM. Results of multicolour flow cytometry and deep-sequencing studies suggest that among patients achieving a complete response, MRD-negative status is associated with significant improvements in progression-free survival and overall survival. Despite the increasing need for MRD testing in patients with MM, considerable heterogeneity in techniques for MRD detection hinders the clinical interpretation of their results. The criteria used to define MRD, strengths and weaknesses of the major types of tests (flow cytometry versus molecular testing), and the optimal sample type (bone marrow aspirate versus peripheral blood) are all unresolved dilemmas in MRD testing. This Review presents an overview of the various techniques for MRD detection in patients with MM. In addition, this article discusses challenges and opportunities for the routine use of MRD testing, possible future directions for clinical trials and implications for drug approval processes.