Implications of detecting serum monoclonal protein by MASS-fix following stem cell transplantation in multiple myeloma.

Measurable residual disease (MRD) assessment by marrow-based next-generation flow cytometry (NGF) following autologous stem cell transplantation (ASCT) may lead to false-negative results due to patchy marrow involvement and extramedullary disease in patients with multiple myeloma. We assessed the value of simultaneous MRD evaluation with NGF and serum matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MASS-FIX). Of all 61 complete responders who were NGF-negative for MRD, around day-100 post ASCT, 59% were MASS-FIX-positive. At median follow-up of 26 months, 69% of MASS-FIX(+)/NGF(-) patients were alive and progression-free versus 96% of MASS-FIX(-)/NGF(-) patients, P = 0·02. MASS-FIX, a simple peripheral blood-based assay complements marrow-based NGF to accurately prognosticate patients with myeloma.