Blood-based MRD testing in multiple myeloma: Update on mass spectrometry methods for detecting the monoclonal immunoglobulin.

Mass spectrometry provides a highly sensitive and specific way to detect low level monoclonal proteins in multiple myeloma. Two main approaches-the intact light chain approach and the clonotypic peptide approach-have been developed and several assays are now commercially available, with some moving into clinical use for routine M-protein testing. Multiple studies have compared the performance of mass spectrometry to established bone marrow-based minimal residual disease (MRD) tests and have provided early insights into its clinical utility in the setting of MRD. This review summarizes the different mass spectrometry methods for M-protein detection, discusses our current understanding of their clinical utility for MRD testing, and describes what the next steps might look like for these promising techniques.