Immunoglobulin M monoclonal gammopathy of undetermined significance (IgM MGUS), a relatively common condition, may progress to Waldenström’s Macroglobulinemia (WM). Speaking from the American Society of Hematology (ASH) 2018 Annual Meeting and Exposition in San Diego, CA, Jonas Paludo, MD, of the Mayo Clinic, Rochester, MN, discusses the immune system profiling of WM and IgM MGUS using CyTOF mass spectrometry, a novel platform coupling mass spectrometry with single-cell flow cytometry using antibody-metal isotope pairs.