Peripheral Measurable Residual Disease Activity Assessment by MALDI-TOF Mass Spectrometry in Patients With Newly...

Mass spectrometry (MS) offers a minimally invasive approach for detecting monoclonal proteins in multiple myeloma (MM), but large prospective evaluations remain limited. We analyzed 3,301 serum samples from 617 patients enrolled in the phase III GMMG-HD7 trial to characterize the analytical performance and clinical relevance of MS-based measurable residual activity. MS reliably distinguished therapeutic antibodies, tracked diagnostic M proteins longitudinally, and demonstrated strong prognostic value across defined time points. MS negativity was associated with superior progression-free survival (PFS), with the greatest separation at later time points (12 months of maintenance: hazard ratio, 0.25 [95% CI, 0.15 to 0.43]; adjusted P < .001). Combined assessment with bone-marrow measurable residual disease (MRD) further refined risk stratification: MS/MRD double-positive patients exhibited the worst PFS, whereas all other groups showed comparably favorable outcomes. MS/MRD concordance increased over time and was influenced by immunoglobulin isotype, with expected immunoglobulin G-recycling-associated early discordance. MS provided accurate M-protein detection and outperformed serum protein electrophoresis at low concentrations, reliably quantifying low-level residual disease. These findings establish serum MS as a sensitive, reproducible, and practical biomarker that complements MRD and supports minimally invasive disease monitoring in MM, with potential integration into future response assessment and risk-adapted treatment strategies.