Immune alterations in multiple myeloma (MM) involve several cell types, and so mass cytometry can be utilized to study a diverse set of single cells simultaneously. Here, Gareth Morgan, MD, PhD, FRCP, FRCPath, of the UAMS Myeloma Institute, Little Rock, AR, discusses the immune system profiling of MM using CyTOF mass spectrometry, the new platform that couples mass spectrometry with single-cell flow cytometry, allowing the observation of significant changes to the immune status post-daratumumab (DARA) treatment.