Introduction: Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) can detect their mass-to-charge(m/z) ratio to capture the low concentration of M protein that serum immunofixation (sIFE) couldn't detect and distinguish therapeutic monoclonal antibody Daratumumab from M protein. Methods: The cross-sectional study included 225 MM patients who were in VGPR or better based on serological and bone marrow tests. 25 of them were MM patients with extramedullary infiltration（EMD. 274 paired serum/bone marrow samples were selected. sIFE and MALDI-TOF MS were used to examine the M protein from peripheral blood. NGF was used in bone marrow samples to examine minimal residual disease (MRD). The threshold of MRD status were set up at the level of 10-5and 10-6 separately. These tests were performed in parallel. 127 patients without EMD accepted autologous hematopoietic stem cell transplantation (ASCT). For these patients, 139 paired serum/bone marrow samples were collected during at least one of the following time: before transplantation (50 paired samples), less than 1 year post ASCT (31 paired samples), more than 1 year post ASCT (58 paired samples). Results: In MM patients without EMD, the concordance of MALDI-TOF MS and sIFE was 69.2%. Comparing to sIFE, the sensitivity of MALDI-TOF MS was 89.1% and the specificity was 54.7%. In MM patients with EMD, the concordance of MALDI-TOF MS and sIFE was 76.5%. Comparing to sIFE, the sensitivity of MALDI-TOF MS was 87.5% and the specificity was 66.7%.In MM patients without EMD, the concordance of MALDI-TOF MS and NGF was 72.9%, the sensitivity of MALDI-TOF MS was 83.8% and the specificity was 60.0% at the 10-5 threshold of NGF. For patients who undergone ASCT, when at the 10-5, the sensitivity of MALDI-TOF MS was 66.7% and the specificity was 35.0%. In the patients who undergone ASCT less than 1 year, MALDI-TOF MS were concordant with NGF for 62.5% at 10−5sensitivity. When at the 10-5 threshold, the sensitivity of MALDI-TOF MS was 80.0% and the specificity was 57.9%. In the patients who undergone ASCT more than 1 year, MALDI-TOF MS were concordant with NGF for 66.7% at 10−5sensitivity. In MM patients with EMD, the concordance of MALDI-TOF MS and NGF was 67.6%, the sensitivity of MALDI-TOF MS was 73.7% and the specificity was 60.0% at the 10-5 or 10-6 threshold of NGF.

MALDI-TOF MS could detect Daratumumab in 91.5% samples during 90 days administration before the samples collection. MALDI-TOF MS could distinguish Daratumumab from M protein in 72.7% IgG-κ samples.

Conclusions: In this study, MALDI-TOF MS showed a highly consistency between the results of SPE/sIFE and MALDI-TOF MS in MM patients with or without EMD. A highly consistency with NGF MRD based on bone marrow and MALDI-TOF MS MRD was presented especially in patients without EMD. MALDI-TOF MS could detect and distinguish Daratumumab from M protein effectively. MALDI-TOF MS is a promising technique.

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2025
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