Clonotypic peptide mass spectrometry to monitor m-protein reduction in patients with relapsed/refractory multiple myeloma from ikema Study

Abstract Background: Relapsed/refractory multiple myeloma (RRMM) remains difficult to monitor with bone marrow aspiration (BMA)–based minimal residual disease (MRD) techniques such as next generation sequencing (NGS) or flow cytometry (NGF), due to the invasive nature of BM aspirates, spatial heterogeneity of disease and calibration failure. M-inSight (Sebia) is an ultrasensitive mass spectrometry assay that sequences patient specific clonotypic peptides from baseline monoclonal (M)-protein and enables longitudinal quantification of these peptides in serum. This blood-based approach offers the potential for a more consistent and patient friendly method to monitor disease burden, particularly in RRMM where BMA MRD evaluation can be limited. The IKEMA phase 3 trial (CT.gov identifier; NCT03275285) evaluated isatuximab plus carfilzomib and dexamethasone (IsaKd) versus Kd alone in RRMM after 1–3 prior lines of therapy, demonstrating superior progression free survival and deeper responses with IsaKd. We performed an exploratory feasibility analysis of M-inSight to monitor serum M protein kinetics in IsaKd–treated patients. Methods: Serum samples (n = 392) from 89 RRMM patients of the IKEMA study collected between 2017 and 2023 were analyzed with M-inSight. All the patients from the IsaKd arm, with available BMA MRD data and serum samples at baseline and upon treatment as well as baseline M-protein concentration meeting the acceptance criteria were selected for this analysis. Clonotypic peptides were identified by LC–MS/MS sequencing of baseline M-protein, and longitudinal serum samples were quantified using high resolution mass spectrometry. M-protein concentrations were tracked at predefined clinical timepoints (prior to cycle initiation), including 12 months (±2 months), to assess assay applicability, longitudinal detectability, and quantitative dynamic range in this RRMM cohort. Results: Clonotypic peptides were successfully identified in 95% of the adequate baseline samples, allowing longitudinal quantification of serum M-protein across the entire RRMM cohort thus demonstrating the robust success rate of this blood-based assay for residual disease detection in RRMM. Importantly, in patients with available BMA NGS data, 99% of those who were MRD-positive at 10⁻⁶ had an M-protein concentration above 0.2 mg/dL (MS pos). Due to limited BMA-MRD sample collection after one year of treatment, it was not possible to find a correlation between MRD BMA neg/MS neg in the range of 0.2 mg/dL as opposed to what was found on NDMM (ASH 2023, poster 3360). When serum samples were available, M-protein reduction average was calculated between 10 and 14 months of treatment. These patients achieved 92% decrease on average (n=36, SD=10%), with 50% of patients (n=18) reaching reductions greater than 99%, corresponding to M-protein concentrations between 0.17 and 28 mg/dL. Furthermore, sustained protein depletion (above 90%, concentrations ranging between 0. 1 mg/dL and 100 mg/dL) was measured on 22 out of these 36 patients even after 3 years after treatment, which is consistent with profound molecular suppression, reflecting disease control. Discussion: This analysis highlights the feasibility of deploying M-inSight for long-term minimally invasive MRD monitoring in a large RRMM trial, where BMA-based assessment is often limited by invasiveness and patchy disease distribution. M-inSight enabled sensitive, reproducible M-protein quantification and detailed monitoring of treatment kinetics across multiple timepoints. Notably, it addressed a key gap in long-term follow-up: in IKEMA, BMA MRD was often not performed after initial assessment of MRD negativity (around 1 year), limiting insights into sustained MRD negativity. M-inSight enabled continued monitoring of clonotypic peptides in serum, delivering data on remission and residual disease up to 3 years post-treatment. This supports sustained MRD surveillance beyond the reach of bone marrow techniques, especially in extended RRMM therapy. Conclusion: M-inSight offers a reliable approach for blood-based MRD assessment in RRMM, with a high success rate for clonotypic peptide identification and longitudinal quantification. Despite the lack of bone marrow samples, it allowed monitoring of low, stable M-protein levels 3 years after treatment. Results support integrating M-inSight into RRMM trials as a robust, patient-friendly alternative to BMA-based MRD techniques.