Comparison of MALDI-TOF mass spectrometry analysis of peripheral blood and bone marrow-based flow cytometry for tracking measurable residual disease in patients with multiple myeloma

Mass spectrometry-based assessment of M protein in peripheral blood during maintenance therapy in multiple myeloma

ABSTRACT

Mass spectrometry (MS) can detect multiple myeloma-derived monoclonal proteins in the peripheral blood (PB) with high sensitivity, potentially serving as a PB assay for measurable residual disease (MRD). This study evaluated the significance of PB MS MRD negativity during posttransplant therapy in patients with newly diagnosed multiple myeloma. Serum samples from 138 patients treated in the phase 3 ATLAS trial of posttransplant maintenance with either carfilzomib, lenalidomide, and dexamethasone, or with lenalidomide alone were analyzed using EXENT MS methodology. We established feasibility of measuring MRD by MS in the PB in the posttransplant setting, despite unavailability of pretreatment calibration samples. There was high agreement between MRD by MS in the PB and paired bone marrow (BM) MRD results at the 10-5 threshold, assessed by either next-generation sequencing (NGS) or multiparameter flow cytometry (MFC) (70% and 67%, respectively). Agreement between PB MS and both BM MRD methods was lowest early after transplant and increased with time. MS negativity was associated with improved progression-free survival (PFS), which, in landmark analysis, reached statistical significance after 18 cycles after transplant. Combined PB/BM MRD negativity by MFC or NGS was associated with superior PFS compared with MRD negativity by only 1 modality. Sustained MS negativity carried similar prognostic performance to sustained BM MRD negativity at the 10-5 threshold. Overall, posttransplant MS assessment was feasible and provided additional prognostic information to BM MRD negativity. Further studies are needed to confirm the role and optimal timing of MS in disease evaluation algorithms. The ATLAS trial is registered at www.clinicaltrials.gov as #NCT02659293.

Liquid biopsy of peripheral blood using mass spectrometry detects primary extramedullary disease in multiple myeloma patients

Multiple myeloma (MM) is the second most prevalent hematological malignancy, characterized by infiltration of the bone marrow by malignant plasma cells. Extramedullary disease (EMD) represents a more aggressive condition involving the migration of a subclone of plasma cells to paraskeletal or extraskeletal sites. Liquid biopsies could improve and speed diagnosis, as they can better capture the disease heterogeneity while lowering patients' discomfort due to minimal invasiveness. Recent studies have confirmed alterations in the proteome across various malignancies, suggesting specific changes in protein classes. In this study, we show that MALDI-TOF mass spectrometry fingerprinting of peripheral blood can differentiate between MM and primary EMD patients. We constructed a predictive model using a supervised learning method, partial least squares-discriminant analysis (PLS-DA) and evaluated its generalization performance on a test dataset. The outcome of this analysis is a method that predicts specifically primary EMD with high sensitivity (86.4%), accuracy (78.4%), and specificity (72.4%). Given the simplicity of this approach and its minimally invasive character, this method provides rapid identification of primary EMD and could prove helpful in clinical practice.

Measurable Residual Disease and Decision-Making in Multiple Myeloma

Measurable (minimal) residual disease (MRD) has already proven to be one of the most important prognostic factors in multiple myeloma (MM). Each improvement in the depth of MRD testing has led to superior discrimination of outcomes, and sustained MRD negativity seems to be paramount to durable responses. Peripheral blood assays to assess for MRD are still under investigation but hold promise as complementary tools to bone marrow MRD assays such as next-generation sequencing and flow cytometry. Herein, the authors explore the evidence and potential benefits and drawbacks of MRD-adapted clinical decision-making in MM.

Monitoring Minimal Residual Disease in Patients with Multiple Myeloma by Targeted Tracking Serum M-Protein Using Mass Spectrometry (EasyM)

PURPOSE

We investigated both the clinical utilities and the prognostic impacts of the clonotypic peptide mass spectrometry (MS)-EasyM, a blood-based minimal residual disease (MRD) monitoring protocol in multiple myeloma.

EXPERIMENTAL DESIGN

A total of 447 sequential serum samples from 56 patients with multiple myeloma were analyzed using EasyM. Patient-specific M-protein peptides were sequenced from diagnostic samples; sequential samples were quantified by EasyM to monitor the M-protein. The performance of EasyM was compared with serum immunofixation electrophoresis (IFE), bone marrow multiparameter flow cytometry (MFC), and next-generation flow cytometry (NGF) detection. The optimal balance of EasyM sensitivity/specificity versus NGF (10-5 sensitivity) was determined and the prognostic impact of MS-MRD status was investigated.

RESULTS

Of the 447 serum samples detected and measured by EasyM, 397, 126, and 92 had time-matching results for comparison with serum IFE, MFC-MRD, and NGF-MRD, respectively. Using a dotp >0.9 as the MS-MRD positive, sensitivity was 99.6% versus IFE and 100.0% versus MFC and NGF. Using an MS negative cutoff informed by ROC analysis (<1.86% of that at diagnosis), EasyM sensitivity remained high versus IFE (88.3%), MFC (85.1%), and NGF (93.2%), whereas specificity increased to 90.4%, 55.8%, and 93.2%, respectively. In the multivariate analysis, older diagnostic age was an independent predictor for progression-free survival [PFS; high risk (HR), 3.15; 1.26-7.86], the best MS-MRD status (MS-MRD negative) was independent predictor for both PFS (HR, 0.25; 0.12-0.52) and overall survival (HR, 0.16; 0.06-0.40).

CONCLUSIONS

EasyM is a highly sensitive and minimal invasive method of MRD monitoring in multiple myeloma; MS-MRD had significant predictive ability for survival outcomes.

[Minimal residual disease assessment and progress in multiple myeloma]

With the rapid iteration of multiple myeloma therapeutics over the last two decades, as well as increasing remission rates and depth of remission in patients, traditional methods for monitoring disease response are insufficient to meet the clinical needs of new drugs. Minimal residual disease (MRD) is a more sensitive test for determining the depth of response, and data from multiple clinical trials and meta-analyses show that a negative MRD correlates with a better prognosis than a traditional complete response. MM is at the forefront of MRD evaluation and treatment. MRD detection methods have been continuously updated. The current MRD assessment has three dimensions: bone marrow-based MRD testing, MRD testing based on images of residual metabolic of focal lesions, and peripheral blood-based MRD testing. The various MRD assessment methods complement one another. The goal of this article is to discuss the currently used MRD assays, the progress, and challenges of MRD in MM, and to provide a reference for clinicians to better use the techniques.

M-protein detection by mass spectrometry for minimal residual disease in multiple myeloma

Multiple myeloma (MM) is characterized by excessive production of monoclonal immunoglobulins (M proteins). Routine screening methods for M proteins to assess prognosis are unable to detect low levels of M proteins produced by residual tumor cells, ie, minimal residual disease (MRD). Assessment of MRD can be conducted by examining residual tumor cells in bone marrow or circulating M proteins. Advances in mass spectrometry have enabled reliable and highly sensitive detection of low abundance serum biomarkers making it a viable and significantly less invasive approach. Mass spectrometry can achieve dynamic monitoring of MRD and identify therapeutic monoclonal antibodies as well as oligoclonal proteins. In this review we summarize mass spectrometry methods in M protein detection and their applications of MRD detection in MM.

Recommendations for the study of monoclonal gammopathies in the clinical laboratory. A consensus of the Spanish Society of Laboratory Medicine and the Spanish Society of Hematology and Hemotherapy. Part I: Update on laboratory tests for the study of monoclonal gammopathies

Monoclonal gammopathies (MG) are characterized by the proliferation of plasma cells that produce identical abnormal immunoglobulins (intact or some of their subunits). This abnormal immunoglobulin component is called monoclonal protein (M-protein), and is considered a biomarker of proliferative activity. The identification, characterization and measurement of M-protein is essential for the management of MG. We conducted a systematic review of the different tests and measurement methods used in the clinical laboratory for the study of M-protein in serum and urine, the biochemistry and hematology tests necessary for clinical evaluation, and studies in bone marrow, peripheral blood and other tissues. This review included literature published between 2009 and 2022. The paper discusses the main methodological characteristics and limitations, as well as the purpose and clinical value of the different tests used in the diagnosis, prognosis, monitoring and assessment of treatment response in MG. Included are methods for the study of M-protein, namely electrophoresis, measurement of immunoglobulin levels, serum free light chains, immunoglobulin heavy chain/light chain pairs, and mass spectrometry, and for the bone marrow examination, morphological analysis, cytogenetics, molecular techniques, and multiparameter flow cytometry.

Aiming for the cure in myeloma: Putting our best foot forward

Frontline therapy for multiple myeloma (MM) is evolving to include novel combinations that can achieve unprecedented deep response rates. Several treatment strategies exist, varying in induction regimen composition, use of transplant and or consolidation and maintenance. In this sea of different treatment permutations, the overarching theme is the powerful prognostic factors of disease risk and achievement of minimal residual disease (MRD) negativity. MM has significant inter-patient variability that requires treatment to be individualized. Risk-adapted and response-adapted strategies which are increasingly being explored to define the extent and duration of therapy, and eventually aim for functional curability. In addition, with T-cell redirection therapies rapidly revolutionizing myeloma treatments, the current standard of care for myeloma will change. This review analyzes the current relevant literature in upfront therapy for fit myeloma patients and provides suggestions for treatment approach while novel clinical trials are maturing.

Measurable residual disease in peripheral blood in myeloma: dream or reality

PURPOSE OF REVIEW

Therapeutic advancements in multiple myeloma have led to increasingly deeper and more durable responses, creating a need for highly sensitive and applicable techniques for measurable residual disease (MRD) assessment. Bone marrow assays can deeply assess for MRD, but it is not conducive to performing frequent and dynamic evaluations, which may be needed for MRD-adapted treatment approaches. Recently, numerous techniques for MRD assessment in peripheral blood have come under investigation, and their integration into routine clinical practice is eagerly anticipated.

RECENT FINDINGS

The identification of circulating tumor cells (CTCs), evaluation of cell-free DNA, and measuring monoclonal protein concentration with mass spectrometry are promising research areas for assessing myeloma in peripheral blood. CTCs assessment and cell-free DNA may carry prognostic significance, but they lack the sensitivity of bone marrow-based techniques. Mass spectrometry has already been implemented in clinical practice in certain centers, but its full potential has yet to be fully realized. This review focuses on recent developments in these fields, emphasizing the potential future roles of these assessments.

SUMMARY

MRD assessment in peripheral blood is still in the development stage but holds promise for not only complementing bone marrow based evaluations but also potential for improving sensitivity.

Detection of serum M-protein in acetonitrile precipitates by MALDI-TOF mass spectrometry: A novel, low-cost methodology

BACKGROUND

Several studies have demonstrated the analytical sensitivity of MALDI-TOF mass spectrometry (MALDI-TOF MS) by immunoenrichment for M-protein analysis. We report the results of a novel, low-cost, reagent-based extraction process using acetonitrile (ACN) precipitation to enrich for κ and λ light chains which can be analysed by MALDI-TOF MS.

METHODS

Institutional Ethics committee approval was obtained. Serum samples from patients with monoclonal gammopathy of undetermined significance (MGUS), multiple myeloma (MM), plasmacytoma, AL amyloidosis and Waldenström macroglobulinemia (WM) underwent ACN precipitation. The images obtained were overlaid on apparently healthy donor serum samples to confirm the presence of M-protein. A sample was considered positive for M-protein if there was a sharp or broad peak within the κ or λ mass/charge (m/z) range: m/z- [M + 2H]2+: 11,550-12,300 Da and λ m/z- [M + 2H]2+: 11,100-11,500 Da. Images were acquired at a m/z range of 10,000-29,000 Da. Corresponding serum protein electrophoresis (SPEP), serum immunofixation electrophoresis (IFE) and serum free light chain (sFLC) assay by nephelometry were performed for all the samples.

RESULTS

Two-hundred-and-two serum samples were included in the study: MM- 184 (91%); AL amyloidosis- 2 (1%); plasmacytoma- 8 (4%); MGUS- 6 (3%) and WM- 2 (1%). All the SPEP positive samples were identified by MALDI-TOF MS. Out of 179 samples positive for M-protein by IFE, MALDI-TOF MS was positive in 176 samples (98%). Compared to IFE, the sensitivity and specificity of M-protein identification by MALDI-TOF MS were 98.3% and 52.2%, respectively.

CONCLUSIONS

This study demonstrates the feasibility of qualitatively identifying M-protein without the need for antibody-based immunoenrichment, making the technique cost-effective.

Minimal Residual Disease in Multiple Myeloma: Past, Present, and Future

Responses to treatment have improved over the last decades for patients with multiple myeloma. This is a consequence of the introduction of new drugs that have been successfully combined in different clinical contexts: newly diagnosed, transplant-eligible or ineligible patients, as well as in the relapsed/refractory setting. However, a great proportion of patients continue to relapse, even those achieving complete response, which underlines the need for updated response criteria. In 2014, the international myeloma working group established new levels of response, prompting the evaluation of minimal residual disease (MRD) for those patients already in complete or stringent complete response as defined by conventional serological assessments: the absence of tumor plasma cells in 100,000 total cells or more define molecular and immunophenotypic responses by next-generation sequencing and flow cytometry, respectively. In this review, we describe all the potential methods that may be used for MRD detection based on the evidence found in the literature, paying special attention to their advantages and pitfalls from a critical perspective.

Implications and prognostic impact of mass spectrometry in patients with newly-diagnosed multiple myeloma

Mass spectrometry (MS) is a promising tool for monitoring monoclonal protein in plasma cell dyscrasias. We included 480 transplant-eligible newly-diagnosed multiple myeloma (MM) patients from the GMMG-MM5 trial (EudraCT No. 2010-019173-16) and performed a retrospective MS analysis at baseline (480 patients) and at the pre-defined, consecutive time points after induction (444 patients), prior to maintenance (305 patients) and after one year of maintenance (227 patients). We found that MS negativity was significantly associated with improved progression-free survival (PFS) even in patients with complete response (CR) at all investigated follow-up time points. The prognostic impact was independent of established risk factors, such as the revised International Staging System. Combining MS and baseline cytogenetics improved the prediction of outcome: MS-positive patients with high-risk cytogenetics had a dismal PFS of 1.9 years (95% confidence interval [CI]: 1.6-2.3 years) from the start of maintenance. Testing the value of sequential MS prior to and after one year of maintenance, patients converting from MS positivity to negativity had an excellent PFS (median not reached) while patients converting from MS negativity to positivity progressed early (median 0.6 years, 95% CI: 0.3-not reached). Among patients with sustained MS positivity, the baseline high-risk cytogenetic status had a significant impact and defined a group with poor PFS. Combining minimal residual disease (MRD) in the bone marrow and MS allowed the identification of double negative patients with a favorable PFS (median 3.33 years, 95% CI: 3.08-not reached) and no overall survival events. Our study provides strong evidence that MS is superior to conventional response monitoring, highlighting the potential of MS to become a new standard. Our data indicate that MS should be performed sequentially and combined with baseline disease features and MRD to improve its clinical value.Clinical Trials Register: EudraCT No. 2010-019173-16.

Graded Depth of Response and Neoplastic Plasma Cell Index as Indicators of Survival Outcomes in Patients With Multiple Myeloma Following Autologous Stem Cell Transplant

OBJECTIVES

With a substantial number of patients with multiple myeloma (MM) experiencing disease relapse, the quest for more sensitive methods to assess deeper responses indicative of cure continues.

METHODS

In this prospective analysis of 170 patients with MM at day 100 after autologous stem cell transplant, we evaluated the predictive value of conventional response, measurable residual disease (MRDTOTAL: the aberrant percentage of plasma cells [PC%] among total bone marrow cells), and neoplastic plasma cell index scores (NPCI: the aberrant PC% of total PCs).

RESULTS

Significantly better progression-free survival (PFS) and overall survival (OS) were observed with deepening conventional response. Conventional response-based stratification within the MRD-positive and MRD-negative subgroups showed a significantly higher PFS (hazard ratio [HR], 3.11; P < .005) and OS (HR, 3.08; P = .01) in the conventional response-positive/MRD-positive group compared with the conventional response-negative/MRD-positive group. Using K-adaptive partitioning to find the optimum threshold for MRD, patients achieving less than 0.001% MRDTOTAL had superior PFS (MRDTOTAL 0.001% to <0.1%: HR, 6.66, P < .005; MRDTOTAL ≥0.1%: HR, 11.52, P < .005) and OS (MRDTOTAL 0.001% to <0.1%: HR, 5.3, P < .05; MRDTOTAL ≥0.1%: HR = 9.21, P < .005). The C index and Akaike information criterion metrics demonstrated the superior performance of the NPCI compared with MRDTOTAL in predicting treatment outcome.

CONCLUSIONS

Progressive deepening of response, conventional as well as MRD, correlates with superior survival outcomes. The NPCI proved to be a superior determinant of survival and can be explored as a better statistic than MRD.

Assessment of Molecular Residual Disease Using Circulating Tumor DNA to Identify Multiple Myeloma Patients at High Risk of Relapse

Background

Despite treatment with high-dose chemotherapy followed by autologous stem cell transplantation (AHCT), patients with multiple myeloma (MM) invariably relapse. Molecular residual disease (MRD)-negativity post-AHCT has emerged as an important prognostic marker predicting the duration of remission. Current techniques for MRD assessment involve bone marrow (BM) aspirate sampling, which is invasive, subject to sample variability and is limited by spatial heterogeneity. We compared the performance of a non-invasive, circulating tumor DNA (ctDNA)-based MRD assay with multiparameter flow cytometry (MFC) of marrow aspirate to predict relapse in AHCT recipients with MM.

Methods

MRD assessment using ctDNA was retrospectively analyzed on 80 plasma samples collected at different time points from 28 patients, post-AHCT. MFC was used to assess MRD from BM biopsy. Individual archived BM aspirate slides or formalin-fixed paraffin-embedded slides from the time of MM diagnosis and matched blood were used to assess MRD at 3 months, post-AHCT, using a personalized, tumor-informed ctDNA assay.

Results

ctDNA was detectable in 70.8% (17/24) of pre-AHCT patients and 53.6% (15/28) of post-AHCT patients (3-month time point). Of the 15 post-AHCT ctDNA-positive patients, 14 relapsed on follow-up. The median PFS for ctDNA-positive patients was 31 months, and that for ctDNA-negative patients was 84 months (HR: 5.6; 95%CI: 1.8-17;p=0.0003). No significant difference in PFS was observed in patients stratified by MFC-based MRD status (HR 1.2; 95%CI: 0.3-3.4;p=0.73). The positive predictive value for ctDNA was also significantly higher than MFC (93.3% vs. 68.4%).

Conclusions

This study demonstrates tumor-informed ctDNA analysis is strongly predictive of MM relapse.

Longitudinal minimal residual disease assessment in multiple myeloma patients in complete remission – results from the NMSG flow-MRD substudy within the EMN02/HO95 MM trial

Background

Multiple myeloma remains an incurable disease with multiple relapses due to residual myeloma cells in the bone marrow of patients after therapy. Presence of small number of cancer cells in the body after cancer treatment, called minimal residual disease, has been shown to be prognostic for progression-free and overall survival. However, for multiple myeloma, it is unclear whether patients attaining minimal residual disease negativity may be candidates for treatment discontinuation. We investigated, if longitudinal flow cytometry-based monitoring of minimal residual disease (flow-MRD) may predict disease progression earlier and with higher sensitivity compared to biochemical assessments.

Methods

Patients from the Nordic countries with newly diagnosed multiple myeloma enrolled in the European-Myeloma-Network-02/Hovon-95 (EMN02/HO95) trial and undergoing bone marrow aspiration confirmation of complete response, were eligible for this Nordic Myeloma Study Group (NMSG) substudy. Longitdudinal flow-MRD assessment of bone marrow samples was performed to identify and enumerate residual malignant plasma cells until observed clinical progression.

Results

Minimal residual disease dynamics were compared to biochemically assessed changes in serum free light chain and M-component. Among 20 patients, reaching complete response or stringent complete response during the observation period, and with ≥3 sequential flow-MRD assessments analysed over time, increasing levels of minimal residual disease in the bone marrow were observed in six cases, preceding biochemically assessed disease and clinical progression by 5.5 months and 12.6 months (mean values), respectively. Mean malignant plasma cells doubling time for the six patients was 1.8 months (95% CI, 1.4–2.3 months). Minimal malignant plasma cells detection limit was 4 × 10–5.

Conclusions

Flow-MRD is a sensitive method for longitudinal monitoring of minimal residual disease dynamics in multiple myeloma patients in complete response. Increasing minimal residual disease levels precedes biochemically assessed changes and is an early indicator of subsequent clinical progression.

Trial registration

NCT01208766

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09184-1.

Minimal Residual Disease Assessment in Multiple Myeloma Patients: Minimal Disease With Maximal Implications

Multiple Myeloma (MM), the second most common hematologic malignancy, has been the target of many therapeutic advances over the past two decades. The introduction of novel agents, such as proteasome inhibitors, immunomodulatory drugs, and monoclonal antibodies, along with autologous hematopoietic stem cell transplantation (ASCT) in the current standard of care, has increased the median survival of myeloma patients significantly. Nevertheless, a curative treatment option continues to elude us, and MM remains an incurable disease, with patients relapsing even after achieving deep conventionally defined responses, underscoring the need for the development of sensitive methods that will allow for proper identification and management of the patients with a higher probability of relapse. Accurate detection of Minimal Residual Disease (MRD) from a bone marrow biopsy represents a relatively new approach of evaluating response to treatment with data showing clear benefit from obtaining MRD(-) status at any point of the disease course. As life expectancy for patients with MM continues to increase and deep responses are starting to become the norm, establishing and refining the role of MRD in the disease course is more relevant than ever. This review examines the different methods used to detect MRD and discusses future considerations regarding the implementation in day-to-day clinical practice and as a prospective primary endpoint for clinical trials.

Relapsed/Refractory Multiple Myeloma in 2020/2021 and Beyond

Despite the challenges imposed by the COVID-19 pandemic, exciting therapeutic progress continues to be made in MM. New drug approvals for relapsed/refractory (RR)MM in 2020/2021 include the second CD38 monoclonal antibody, isatuximab, the first BCMA-targeting therapy and first-in-class antibody-drug conjugate (ADC) belantamab mafodotin, the first BCMA-targeting CAR T cell product Idecabtagen-Vicleucel (bb2121, Ide-Cel), the first in-class XPO-1 inhibitor selinexor, as well as the first-in-class anti-tumor peptide-drug conjugate, melflufen. The present introductory article of the Special Issue on "Advances in the Treatment of Relapsed and Refractory Multiple Myeloma: Novel Agents, Immunotherapies and Beyond" summarizes the most recent registration trials and emerging immunotherapies in RRMM, gives an overview on latest insights on MM genomics and on tumor-induced changes within the MM microenvironment, and presents some of the most promising rationally derived future therapeutic strategies.

Minimal Residual Disease in Myeloma: Application for Clinical Care and New Drug Registration

The development of novel agents has transformed the treatment paradigm for multiple myeloma, with minimal residual disease (MRD) negativity now achievable across the entire disease spectrum. Bone marrow-based technologies to assess MRD, including approaches using next-generation flow and next-generation sequencing, have provided real-time clinical tools for the sensitive detection and monitoring of MRD in patients with multiple myeloma. Complementary liquid biopsy-based assays are now quickly progressing with some, such as mass spectrometry methods, being very close to clinical use, while others utilizing nucleic acid-based technologies are still developing and will prove important to further our understanding of the biology of MRD. On the regulatory front, multiple retrospective individual patient and clinical trial level meta-analyses have already shown and will continue to assess the potential of MRD as a surrogate for patient outcome. Given all this progress, it is not surprising that a number of clinicians are now considering using MRD to inform real-world clinical care of patients across the spectrum from smoldering myeloma to relapsed refractory multiple myeloma, with each disease setting presenting key challenges and questions that will need to be addressed through clinical trials. The pace of advances in targeted and immune therapies in multiple myeloma is unprecedented, and novel MRD-driven biomarker strategies are essential to accelerate innovative clinical trials leading to regulatory approval of novel treatments and continued improvement in patient outcomes.

The 2020 BMT CTN Myeloma Intergroup Workshop on Immune Profiling and Minimal Residual Disease Testing in Multiple Myeloma

The fifth annual Blood and Marrow Transplant Clinical Trials Network Myeloma Intergroup Workshop on Immune Profiling and Minimal Residual Disease Testing in Multiple Myeloma was conducted as one of the American Society of Hematology Annual Meeting Scientific Workshops on Thursday December 3, 2020. This workshop focused on four main topics: (1) integrating minimal residual disease into clinical trial design and practice; (2) the molecular and immunobiology of disease evolution and progression in myeloma; (3) adaptation of next-generation sequencing, next-generation flow cytometry, and cytometry by time of flight techniques; and (4) chimeric antigen receptor T-cell and other cellular therapies for myeloma. In this report, we provide a summary of the workshop presentations and discuss future directions in the field.

Minimal Residual Disease in Multiple Myeloma: Ready for Prime Time?

ABSTRACT

Minimal residual disease (MRD) techniques are essential to identify the small clonal fraction within and outside the bone marrow. In the last years, evidence regarding their prognostic role for the evaluation of the depth of response of current treatment strategies has grown rapidly. Consequently, MRD was incorporated in an increasing number of clinical trials for multiple myeloma patients, also as primary endpoint, and even to guide therapeutic choices. A robust correlation between MRD negativity and survival was established. Yet, several issues regarding MRD evaluation remain to be addressed: from the optimal and more cost-effective techniques for its assessment and its harmonization worldwide to its use in clinical practice to its impact on treatment modulation. This review focuses on the available evidence supporting the use of MRD status for the management of multiple myeloma patients and on open issues that still need an answer.

Therapeutic Advances Propelled by Deciphering Tumor Biology and Immunology-Highlights of the 8th Heidelberg Myeloma Workshop

Simple Summary

The 8th Heidelberg Myeloma Workshop was held on 16–17 April 2021 at the University Hospital Heidelberg, Germany. The main topics of the meeting were diagnostics and prognostic factors of early-phase multiple myeloma (MM), the role of immunotherapy, as well as the biology and genomics of MM. This manuscript reports on recent advances in MM research and points out future directions.

Abstract

The diagnostics and treatment of newly diagnosed and relapsed MM are continuously evolving. While advances in the field of (single cell) genetic analysis now allow for characterization of the disease at an unprecedented resolution, immunotherapeutic approaches and MRD testing are at the forefront of the current clinical trial landscape. Here, we discuss research progress aimed at gaining a better understanding of this heterogenous disease entity, presented at the 8th Heidelberg Myeloma Workshop. We address the questions of whether biology can guide treatment decisions in MM and how assessment for measurable residual disease can help physicians in clinical decision-making. Finally, we summarize current developments in immunotherapeutic approaches that promise improved patient outcomes for MM patients. Besides summarizing key developments in MM research, we highlight perspectives given by key opinion leaders in the field.

Minimal Residual Disease in Multiple Myeloma: Potential for Blood-Based Methods to Monitor Disease

In recent years, the life expectancy of Multiple Myeloma (MM) patients has substantially improved, but this cancer remains incurable with increasing incidence in the developed world. Most MM patients will eventually relapse due to residual drug-resistant cancerous cells that survive treatment, commonly referred to as minimal residual disease (MRD). Methods to improve MRD detection in MM patients are generating considerable interest as a means of monitoring patients' response to treatment. In clinical laboratories, these methods currently require bone marrow aspirates which are invasive and frequently miss detection of localised disease due to the spatial heterogeneity of disease infiltration. By simplifying serial sampling and allowing for the detection of extramedullary disease, a blood-based method could significantly impact treatment duration and intensity and minimise chemotherapy-induced toxicity. This review will describe the current blood-based techniques available to detect MRD in MM and compare their potential to evaluate patient prognosis and drive therapeutic decisions.

Using quantitative immunoprecipitation mass spectrometry (QIP-MS) to identify low level monoclonal proteins

Mass spectrometry has recently been proposed as a novel sensitive screening tool for monoclonal gammopathies. In a small study we have tested the ability of quantitative immunoprecipitation mass spectrometry (QIP-MS) to identify low level monoclonal immunoglobulins not currently detected by the initial serum protein electrophoresis (SPEP) screen. QIP-MS positively identified the primary monoclonal immunoglobulins in all 11 patient samples alongside additional monoclonal immunoglobulins in a subset of patient samples. We conclude that QIP-MS has clinical utility as a first-line screening tool for monoclonal gammopathy investigation, identifying monoclonality in patients with higher sensitivity and resolution compared to the current standard methods.

MRD Assessment in Multiple Myeloma: Progress and Challenges

PURPOSE OF REVIEW

Over the last decade, the development of effective treatment approaches for multiple myeloma (MM) has been associated with higher response rates and longer survival. In patients who achieve complete response, several high sensitivity techniques have been studied to assess minimal residual disease (MRD) and detect residual neoplastic cells within the bone marrow (by flow cytometry or molecular biology techniques) or outside the bone marrow (by imaging or circulating disease markers in the peripheral blood). This is of utmost importance, since residual disease can drive clinical relapse. This review focuses on the progress made in the assessment of MRD in MM.

RECENT FINDINGS

The achievement of MRD negativity after therapy is considered prognostically important for MM patients, and data from clinical trials and meta-analyses have confirmed that it is strongly associated with better survival. Along with well-known techniques, such as next-generation sequencing (NGS), next-generation flow (NGF), and positron emission tomography/computed tomography (PET/CT), other methods such as mass spectrometry (MS) and circulating tumor cells are under study. Intensive treatment regimens at diagnosis can lead up to 70% of MRD negativity in MM patients, although the current proportion of curable patients is still unknown. Today, clinicians who treat MM deal with MRD assessment in routine clinical practice. Its appropriate use in therapeutic decision making may be the most fascinating and challenging issue to be addressed over the next few years.

Clinical Mass Spectrometry Approaches to Myeloma and Amyloidosis

The diagnosis of myeloma and other plasma cell disorders has traditionally been done with the aid of electrophoretic methods, whereas amyloidosis has been characterized by immunohistochemistry. Mass spectrometry has recently been established as an alternative to these traditional methods and has been proved to bring added benefit for patient care. These newer mass spectrometry-based methods highlight some of the key advantages of modern proteomic methods and how they can be applied to the routine care of patients.

Minimal residual disease in multiple myeloma: defining the role of next generation sequencing and flow cytometry in routine diagnostic use

For patients diagnosed with multiple myeloma (MM) there have been significant treatment advances over the past decade, reflected in an increasing proportion of patients achieving durable remissions. Clinical trials repeatedly demonstrate that achieving a deep response to therapy, with a bone marrow assessment proving negative for minimal residual disease (MRD), confers a significant survival advantage. To accurately assess for minute quantities of residual cancer requires highly sensitive methods; either multiparameter flow cytometry or next generation sequencing are currently recommended for MM response assessment. Under optimal conditions, these methods can detect one aberrant cell amongst 1,000,000 normal cells (a sensitivity of 10^-6). Here, we will review the practical use of MRD assays in MM, including challenges in implementation for the routine diagnostic laboratory, standardisation across laboratories and clinical trials, the clinical integration of MRD status assessment into MM management and future directions for ongoing research.

Using MALDI-TOF mass spectrometry in peripheral blood for the follow up of newly diagnosed multiple myeloma patients treated with daratumumab-based combination therapy

BACKGROUND

Daratumumab-based combination therapies have shown high rates of complete response (CR) and minimal residual disease negativity in patients with multiple myeloma. However, daratumumab, an IgGκ monoclonal antibody, interferes with electrophoretic techniques making it difficult to reliably define residual disease versus CR, especially in patients with IgGκ multiple myeloma.

METHODS

Enrichment with polyclonal sheep antibody-coated magnetic microparticles combined with MALDI-TOF mass spectrometry (MALDI-TOF MS) analysis was used to detect M-proteins in serial samples from newly diagnosed multiple myeloma patients treated with daratumumab-based therapy. The performance of the MALDI-TOF MS assay was compared to that of a routine test panel (serum protein electrophoresis (SPEP), immunofixation (IFE) and serum free light chain (FLC)).

RESULTS

Comparison of MALDI-TOF MS to SPEP/IFE/FLC showed a concordance of 84.9% (p < 0.001). When MALDI-TOF MS and FLC results were combined, the M-protein detection rate was the same or better than the routine test panel. For the 9 patients who obtained CR during follow-up, MALDI-TOF MS detected an M-protein in 46% of subsequent samples. Daratumumab could be distinguished from the M-protein in 215/222 samples.

CONCLUSION

MALDI-TOF MS is useful in assessing CR in patients treated with monoclonal antibody-based therapies.

Mass spectrometry for the evaluation of monoclonal proteins in multiple myeloma and related disorders: an International Myeloma Working Group Mass Spectrometry Committee Report

Plasma cell disorders (PCDs) are identified in the clinical lab by detecting the monoclonal immunoglobulin (M-protein) which they produce. Traditionally, serum protein electrophoresis methods have been utilized to detect and isotype M-proteins. Increasing demands to detect low-level disease and new therapeutic monoclonal immunoglobulin treatments have stretched the electrophoretic methods to their analytical limits. Newer techniques based on mass spectrometry (MS) are emerging which have improved clinical and analytical performance. MS is gaining traction into clinical laboratories, and has replaced immunofixation electrophoresis (IFE) in routine practice at one institution. The International Myeloma Working Group (IMWG) Mass Spectrometry Committee reviewed the literature in order to summarize current data and to make recommendations regarding the role of mass spectrometric methods in diagnosing and monitoring patients with myeloma and related disorders. Current literature demonstrates that immune-enrichment of immunoglobulins coupled to intact light chain MALDI-TOF MS has clinical characteristics equivalent in performance to IFE with added benefits of detecting additional risk factors for PCDs, differentiating M-protein from therapeutic antibodies, and is a suitable replacement for IFE for diagnosing and monitoring multiple myeloma and related PCDs. In this paper we discuss the IMWG recommendations for the use of MS in PCDs.

Measurable residual disease in multiple myeloma and light chain amyloidosis: more than meets the eye

The emergence of highly effective multiple myeloma (MM) treatments may bring cure within reach and highlights the need for highly sensitive measurable residual disease (MRD) techniques to replace conventional response assessments. MRD is being incorporated as an endpoint in an increasing number of studies and had been repeatedly shown to be both a predictive marker of response to treatment and a prognostic marker for future relapse. However, those results should be cautiously interpreted due to non-uniform reporting and the need for longer follow up to assess for sustained MRD negativity. This review aims to critically analyze the key MRD aspects including the current evidence supporting the use of MRD in clinical practice and the pitfalls of the various methods used to assess MRD. The utility of MRD for light chain (AL) amyloidosis will also be discussed.

Minimal Residual Disease in Multiple Myeloma: State of the Art and Future Perspectives

Minimal residual disease (MRD) detection represents a sensitive tool to appropriately measure the response obtained with therapies for multiple myeloma (MM). The achievement of MRD negativity has superseded the conventional complete response (CR) and has been proposed as a surrogate endpoint for progression-free survival and overall survival. Several techniques are available for the detection of MRD inside (next-generation sequencing, flow cytometry) and outside (PET/CT, magnetic resonance) the bone marrow, and their complementary use allows a precise definition of the efficacy of anti-myeloma treatments. This review summarizes MRD data and results from previous clinical trials, highlights open issues related to the role of MRD in MM and discusses how MRD could be implemented in clinical practice to inform on patient prognosis and drive therapeutic decisions.

Measurable residual disease in multiple myeloma: ready for clinical practice?

The landscape of multiple myeloma (MM) has changed considerably in the past two decades regarding new treatments, insight into disease biology and innovation in the techniques available to assess measurable residual disease (MRD) as the most accurate method to evaluate treatment efficacy. The sensitivity and standardization achieved by these techniques together with unprecedented rates of complete remission (CR) induced by new regimens, raised enormous interest in MRD as a surrogate biomarker of patients' outcome and endpoint in clinical trials. By contrast, there is reluctance and general lack of consensus on how to use MRD outside clinical trials. Here, we discuss critical aspects related with the implementation of MRD in clinical practice.