Smoldering multiple myeloma: natural history and recognition of an evolving type

Round Table Discussion on Optimal Clinical Trial Design in Precursor Multiple Myeloma

SUMMARY

While the current approach to precursor hematologic conditions is to "watch and wait," this may change with the development of therapies that are safe and extend survival or delay the onset of symptomatic disease. The goal of future therapies in precursor hematologic conditions is to improve survival and prevent or delay the development of symptomatic disease while maximizing safety. Clinical trial considerations in this field include identifying an appropriate at-risk population, safety assessments, dose selection, primary and secondary trial endpoints including surrogate endpoints, control arms, and quality-of-life metrics, all of which may enable more precise benefit-risk assessment.

Smoldering Multiple Myeloma: Observation Versus Control Versus Cure

Smoldering multiple myeloma (SMM) is an intermediate clinical stage in the spectrum of monoclonal plasma cell disorders. It represents a heterogeneous clinically defined condition in which some patients (approximately 50%) have monoclonal gammopathy of undetermined significance (premalignancy), and some (approximately 50%) have multiple myeloma (biologic malignancy). Using specific prognostic factors, patients with SMM, in whom malignant transformation has already likely occurred, can be identified. These patients are considered to have high-risk SMM. Patients with newly diagnosed high-risk SMM are candidates for early intervention with lenalidomide or lenalidomide plus dexamethasone for 2 years, or enrollment in clinical trials.

SLiM CRAB criteria revisited: temporal trends in prognosis of patients with smoldering multiple myeloma who meet the definition of ‘biomarker-defined early multiple myeloma’—a systematic review with meta-analysis

Background

Biomarker-defined patients with smoldering multiple myeloma (SMM) were included in the diagnostic category of multiple myeloma (MM) by the International Myeloma Working Group (IMWG) in 2014. This includes ≥60% bone marrow plasma cells (BMPCs), free light chain ratio (FLCratio) ≥100, and >1 MRI-defined ≥5 mm focal lesion, also called SLiM CRAB MM. We examined whether the risk of progression of SLiM CRAB MM patients to CRAB positive MM described in recent studies differs from that reported in earlier studies published before the introduction of the new diagnostic criteria.

Methods

We conducted a systematic review with meta-analysis, and included studies on Embase and PubMed (01/01/2010-01/11/2022), selecting studies with digitizable progression curves. Inconsistent studies were excluded. We created forest plots using random effects models from digitized and published data and Kaplan-Meier curves. Main outcomes were median time to progression (TTP), 2-year progression risk, and odds ratios (ORs) comparing 2-year progression risks.

Findings

Our meta-analysis including 11 studies with 3482 patients found an approximately 3-fold longer TTP and 50% lower 2-year progression risk of SliM CRAB MM patients in recent (published after 2014) compared with earlier studies. Median TTP in patients with ≥60% BMPCs was 30.31 months [18.71-62.93] in recent compared with 9.20 months [6.02-15.56] in earlier studies; the 2-year progression risk was 45.45% [20.12-62.75] compared with 86.21% [65.74-94.45] in the respective time periods. In patients with a FLCratio ≥ 100, the median TTP was 48.06 months [40.51-64.91] vs. 15.33 months [9.38-19.10], and the 2-year progression risk was 31.61% [25.30-37.39] vs. 73.00% [62.39-80.62] in recent and earlier studies, respectively. Tests for heterogeneity showed that the two time periods differed significantly in their ORs when comparing patients who met the high-and low risk criteria. No appropriate recent studies on focal lesions have been published.

Interpretation

Recent studies show significantly improved prognosis of biomarker-defined MM with ≥60% BMPCs and FLCratio ≥ 100. This warrants careful evaluation for signs of progression before treatment initiation.

Funding

Funding was provided by the Austrian Forum against Cancer.

Smoldering multiple myeloma current treatment algorithms

Smoldering multiple myeloma (SMM) is an asymptomatic condition that occupies a space between monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma (MM) along the spectrum of clonal plasma cell proliferative disorders. It is not a biologic intermediate stage between MGUS and MM, but rather represents a heterogeneous clinically defined condition in which some patients (approximately two-thirds) have MGUS (pre-malignancy), and some (approximately one-third) have MM (biologic malignancy). Unfortunately, no single pathologic or molecular feature can reliably distinguish these two groups of patients. For purposes of practice and clinical trials, specific risk factors are used to identify patients with SMM in whom malignant transformation has already likely occurred (high risk SMM). Patients with newly diagnosed high risk SMM should be offered therapy with lenalidomide or lenalidomide plus dexamethasone (Rd) for 2 years, or enrollment in clinical trials. Patients with low risk SMM should be observed without therapy every 3–4 months.

How I approach smoldering multiple myeloma

The current standard of care in smoldering multiple myeloma (SMM) is close surveillance, outside of clinical trials. Efforts are being made to understand the pathobiologic process that leads to the progression of SMM to active MM. This review provides a critical description of available data, including risk factors and risk models of progression, as well as clinical trials investigating interventions for this patient population. We describe 2 cases in which patients were seen before the concept of a myeloma-defining event was established. Today, based on the International Myeloma Working Group criteria, both patients would have been identified as experiencing myeloma-defining events, and therapy would have been initiated. These cases show that occasionally, patients can undergo observation only, even when they exceed criteria for high-risk SMM.

The Dynamics of Nucleotide Variants in the Progression from Low-Intermediate Myeloma Precursor Conditions to Multiple Myeloma: Studying Serial Samples with a Targeted Sequencing Approach

Simple Summary

Multiple myeloma (MM), characterized by the expansion of plasma cells in the bone marrow, is the second most common hematological malignancy. This incurable cancer is consistently preceded by non-malignant asymptomatic precursor conditions known as monoclonal gammopathy of undetermined significance (MGUS) and/or smoldering multiple myeloma (SMM). These pre-stages are relatively frequent, but only a select percentage of them will progress to MM. However, it is still not possible to individually predict when and which patients will develop MM. Therefore, this study aimed to investigate the mutational profile in the progression in serial bone marrow samples with a custom targeted sequencing panel, designed to detect variants in myeloma-related genes. Remarkably, almost all variants identified in the MM samples were also already present in the pre-stages, sometimes even many years before the progression. These results provide new important insights into the molecular mechanisms of the precursor conditions and progression to MM.

Abstract

Multiple myeloma (MM), or Kahler’s disease, is an incurable plasma cell (PC) cancer in the bone marrow (BM). This malignancy is preceded by one or more asymptomatic precursor conditions, monoclonal gammopathy of undetermined significance (MGUS) and/or smoldering multiple myeloma (SMM). The molecular mechanisms and exact cause of this progression are still not completely understood. In this study, the mutational profile underlying the progression from low–intermediate risk myeloma precursor conditions to MM was studied in serial BM smears. A custom capture-based sequencing platform was developed, including 81 myeloma-related genes. The clonal evolution of single nucleotide variants and short insertions and deletions was studied in serial BM smears from 21 progressed precursor patients with a median time of progression of six years. From the 21 patients, four patients had no variation in one of the 81 studied genes. Interestingly, in 16 of the 17 other patients, at least one variant present in MM was also detected in its precursor BM, even years before progression. Here, the variants were present in the pre-stage at a median of 62 months before progression to MM. Studying these paired BM samples contributes to the knowledge of the evolutionary genetic landscape and provides additional insight into the mutational behavior of mutant clones over time throughout progression.

Risk Stratification and Treatment in Smoldering Multiple Myeloma

Smoldering multiple myeloma is a heterogeneous asymptomatic precursor to multiple myeloma. Since its identification in 1980, risk stratification models have been developed using two main stratification methods: clinical measurement-based and genetics-based. Clinical measurement models can be subdivided in three types: baseline measurements (performed at diagnosis), evolving measurements (performed over time during follow-up appointments), and imaging (for example, magnetic resonance imaging). Genetic approaches include gene expression profiling, DNA/RNA sequencing, and cytogenetics. It is important to accurately distinguish patients with indolent disease from those with aggressive disease, as clinical trials have shown that patients designated as “high-risk of progression” have improved outcomes when treated early. The risk stratification models, and clinical trials are discussed in this review.

Advances in MGUS diagnosis, risk stratification, and management: introducing myeloma-defining genomic events

In the 1960s, Dr Jan Waldenström argued that patients who had monoclonal proteins without any symptoms or evidence of end-organ damage represented a benign monoclonal gammopathy. In 1978, Dr Robert Kyle introduced the concept of “monoclonal gammopathy of undetermined significance” (MGUS) given that, at diagnosis, it was not possible with available methods (ie, serum protein electrophoresis to define the concentration of M-proteins and microscopy to determine the plasma cell percentage in bone marrow aspirates) to determine which patients would ultimately progress to multiple myeloma. The application of low-input whole-genome sequencing (WGS) technology has circumvented previous problems related to volume of clonal plasma cells and contamination by normal plasma cells and allowed for the interrogation of the WGS landscape of MGUS. As discussed in this chapter, the distribution of genetic events reveals striking differences and the existence of 2 biologically and clinically distinct entities of asymptomatic monoclonal gammopathies. Thus, we already have genomic tools to identify “myeloma-defining genomic events,” and consequently, it is reasonable to consider updating our preferred terminologies. When the clinical field is ready to move forward, we should be able to consolidate current terminologies—from current 7 clinical categories: low-risk MGUS, intermediate-risk MGUS, high-risk MGUS, low-risk smoldering myeloma, intermediate-risk smoldering myeloma, high-risk smoldering myeloma, and multiple myeloma—to future 3 genomic-based categories: monoclonal gammopathy, early detection of multiple myeloma (in which myeloma-defining genomic events already have been acquired), and multiple myeloma (patients who are already progressing and clinically defined cases). Ongoing investigations will continue to advance the field.

Gene Expression Analysis of the Bone Marrow Microenvironment Reveals Distinct Immunotypes in Smoldering Multiple Myeloma Associated to Progression to Symptomatic Disease

Background

We previously reported algorithms based on clinical parameters and plasma cell characteristics to identify patients with smoldering multiple myeloma (SMM) with higher risk of progressing who could benefit from early treatment. In this work, we analyzed differences in the immune bone marrow (BM) microenvironment in SMM to better understand the role of immune surveillance in disease progression and to identify immune biomarkers associated to higher risk of progression.

Methods

Gene expression analysis of BM cells from 28 patients with SMM, 22 patients with monoclonal gammopathy of undetermined significance (MGUS) and 22 patients with symptomatic MM was performed by using Nanostring Technology.

Results

BM cells in SMM compared to both MGUS and symptomatic MM showed upregulation of genes encoding for key molecules in cytotoxicity. However, some of these cytotoxic molecules positively correlated with inhibitory immune checkpoints, which may impair the effector function of BM cytotoxic cells. Analysis of 28 patients with SMM revealed 4 distinct clusters based on immune composition and activation markers. Patients in cluster 2 showed a significant increase in expression of cytotoxic molecules but also inhibitory immune checkpoints compared to cluster 3, suggesting the presence of cytotoxic cells with an exhausted phenotype. Accordingly, patients in cluster 3 had a significantly longer progression free survival. Finally, individual gene expression analysis showed that higher expression of TNF superfamily members (TNF, TNFAIP3, TNFRSF14) was associated with shorter progression free survival.

Conclusions

Our results suggest that exhausted cytotoxic cells are associated to high-risk patients with SMM. Biomarkers overexpressed in patients with this immune gene profile in combination with clinical parameters and PC characterization may be useful to identify SMM patients with higher risk of progression.

Assessing the prognostic utility of smoldering multiple myeloma risk stratification scores applied serially post diagnosis

The Mayo-2018 smoldering multiple myeloma (SMM) risk score is used routinely in the clinical setting but has only been validated at diagnosis. In SMM patients, the progression risk decreases over time. However, the utility of applying risk stratification models after diagnosis is unknown. We retrospectively studied 704 SMM patients and applied the Mayo 2018 and IMWG-2020 risk stratification models at annual landmark timepoints up to 5 years post diagnosis. The Mayo-2018 and IMWG-2020 models reliably stratified patients based on progression risk when applied post diagnosis. The respective 2-year progression risk in Mayo-2018 high risk patients versus IMWG-2020 intermediate-high risk patients was 51% versus 62% at the 1-year landmark and 47% versus 45% at the 4-year landmark. We showed that patients categorized at Mayo-2018 high-risk at follow-up had a similar risk of progression if the baseline risk assessment was low-intermediate versus high-risk (HR 1.04, 95% CI 0.46-2.36, p = 0.931 at 5-year landmark). Patients migrating to a higher risk category during follow up had a higher progression risk compared to patients with stable/decreased risk categorization. Our findings support the use of these risk scores post-diagnosis and suggest that patients evolving to a high-risk category may benefit from early intervention therapeutic approaches.

The benefits of early intervention using lenalidomide for high-risk smoldering multiple myeloma: emerging data and its promising clinical impact

INTRODUCTION

Multiple myeloma is preceded by the early stages: monoclonal gammopathy of unknown significance (M.G.U.S.) and smoldering myeloma (S.M.M.), which are less genomically complex and where patients are overall healthier with preserved quality of life.

AREAS COVERED

This review focuses on the current evidence in risk stratification and initial therapy for these patients with the goal to delay progression to and/or cure multiple myeloma.

EXPERT OPINION

Advances in the understanding of the factors that contribute to myeloma evolution coupled with new therapeutics that have high efficacy and limited toxicity have revolutionized our approach to early myeloma. Although our current recommendation continues to be to observe S.M.M. outside of clinical trials, the clinical benefit of lenalidomide sets the stage for combinations with immunotherapy, which, in our opinion, will likely lead to regulatory approvals and more widespread treatment of early myeloma.

Smoldering Myeloma Treatment: Who, What, and When

ABSTRACT

Smoldering multiple myeloma (MM) is a clonal plasma cell disorder characterized by excess marrow involvement and immunoglobulin production. It is the precursor of MM, differing by the lack of end-organ damage. Smoldering MM encompasses a heterogeneous group of patients, with a median risk of progression to active disease of 50% in the first 5 years. Until recently, the standard of care would dictate observation off therapy until the development of end-organ damage. The recognition of high-risk and ultrahigh-risk subgroups of smoldering MM, with more likely evolution to MM, has led to earlier initiation of therapy in the disease course. Ongoing studies to define the ideal timing and patient population are underway, as well as identification of which agents would be of greatest benefit, as the armamentarium for MM continues to grow.

[Monoclonal gammopathy of undetermined significance and evolution to myeloma: Experience in 153 patients]

INTRODUCTION

Based on risk factors, the Mayo Clinic Multiple Myeloma Group (MCMMG) established a model of progression from monoclonal gammopathy of undetermined significance (MGUS) to multiple myeloma (MM) at 20 years. It is also described that MGUS with a progressive increase of monoclonal protein (M-protein) and/or immunoparesis (IMP) may be more predisposed to progress to myeloma. Our objective was to make a review of MGUS, to see how those who presented IMP and/or progression of their M-protein, contrasting them with MGUS that presented intermediate/high and high risk according to MCMMG.

METHODOLOGY AND MATERIALS

A review of the MGUS objectified during the realization of a serum proteinogram (SPEP) was carried out during 2010-2014, in our area. Serum immunoglobulins, serum immunofixation (IFs), and serum free light chain ratio (FLCr) were determined for all MGUS.

RESULTS

Of the 153 MGUS that are followed up for 4 years, 6 progress to MM. Of these 6 MM, 5 progress from MGUS with intermediate/high risk taking into account the MCMMG. Of these 5, 3 have IMP or progression of their M-protein. 2 present IMP plus progression of their M-protein. The sixth MM evolves from a MGUS without any risk factor, but with progression of its M-protein plus IMP.

CONCLUSIONS

IMP and/or M-protein progression are important risk factors to be taken into account in the MGUS, in the first years after diagnosis, due to their possible evolution to MM.

Smoldering multiple myeloma - Past, present, and future

Smoldering multiple myeloma (SMM) routinely precedes the development of multiple myeloma. While some patients experience aggressive disease, others have more indolent courses akin to those with monoclonal gammopathy of undetermined significance. Much effort has been made to understand the pathobiological basis of this heterogeneity. Scientific advancements have led to the emergence of various clinical and genomic markers of relevance, translating into evolution of disease definitions over time. More recently, the interest in manipulation of biological pathways has intensified in a bid to stall or halt disease progression. Studies with lenalidomide have exemplified the promise of early intervention, whereas numerous therapeutic approaches remain the subject of ongoing clinical investigation. This review summarizes the historic progress made in defining SMM as a distinct clinicopathologic entity, provides a critical appraisal of the evidence guiding risk assessment, and suggests a pragmatic approach to its modern-day management. Finally, an overview of developments on the horizon is also provided.

Testing Mayo Clinic's New 20/20/20 Risk Model in Another Cohort of Smoldering Myeloma Patients: A Retrospective Study

Background—smoldering multiple myeloma (SMM) risk of progression to multiple myeloma (MM) is highly heterogeneous and several models have been suggested to predict this risk. Lakshman et al. recently proposed a model based on three biomarkers: bone marrow plasma cell (BMPC) percentage > 20%, free light chain ratio (FLCr) > 20 and serum M protein > 20 g/L. The goal of our study was to test this “20/20/20” model in our population and to determine if similar results could be obtained in another cohort of SMM patients. Method—we conducted a retrospective, single center study with 89 patients diagnosed with SMM between January 2008 and December 2019. Results—all three tested biomarkers were associated with an increased risk of progression: BMPC percentage ≥ 20% (hazard ratio [HR]: 4.28 [95%C.I., 1.90–9.61]; p < 0.001), serum M protein ≥ 20 g/L (HR: 4.20 [95%C.I., 1.90–15.53]; p = 0.032) and FLCr ≥ 20 (HR: 3.25 [95%C.I., 1.09–9.71]; p = 0.035). The estimated median time to progression (TTP) was not reached for the low and intermediate risk groups and was 29.1 months (95%C.I., 3.9–54.4) in the high-risk group (p = 0.006). Conclusions—the 20/20/20 risk stratification model adequately predicted progression in our population and is easy to use in various clinical settings.

Progress in the Management of Smoldering Multiple Myeloma

PURPOSE OF REVIEW

Smoldering multiple myeloma (SMM) is defined as an asymptomatic clonal proliferation of pre-malignant plasma cells and an increased risk of progression to multiple myeloma (MM) relative to monoclonal gammopathy of undetermined significance. Whether patients with SMM should be treated prior to development of symptomatic disease is fiercely debated and is a highly active area of research.

RECENT FINDINGS

The ECOG E3A06 study demonstrated that early treatment with lenalidomide significantly reduced the risk of progression to MM compared to observation in patients with high risk SMM. The IMWG recently validated a risk stratification model to include cytogenetics and a personalized risk calculator for individual patients. Beyond this, molecular genomic aberrations and immunological phenomena that promote progression from asymptomatic disease to MM have been recently characterized and may help to more precisely identify patients who are most suitable for early intervention. As highly effective and tolerable therapies for plasma cell disorders evolve, the field is approaching a paradigm shift that involves the adoption of intervention for patients with SMM who are at high risk for progression to symptomatic myeloma in order to prevent morbidity and mortality. This review highlights our current understanding of the biology of patients with SMM, clarifies the rationale for early intervention, and summarizes early results of various treatment strategies for patients with high-risk smoldering myeloma.

Comparative evaluation of involved free light chain and monoclonal spike as markers for progression from monoclonal gammopathy of undetermined significance to multiple myeloma

Monoclonal gammopathy of undetermined significance (MGUS) is a premalignant clonal plasma cell disorder, with a 1% yearly risk of progression to multiple myeloma (MM). Evolution of M-spike and serum free light chain (sFLC) during follow-up could identify patients at high risk of progression. In this region-wide study, including 4756 individuals, 987 patients with MGUS were identified, and baseline factors as well as evolving involved FLC (iFLC) were evaluated as potential markers for risk of progression from MGUS to MM. Furthermore, evolving iFLC and M-spike were assessed quarterly for a median of 5 years. At baseline, patients that progressed had significantly higher iFLC compared to non-progressors. The risk factors of M-spike >1.5 g/dL, age >65 years and iFLC >100 mg/L were all independently associated with increased risk of MGUS to MM progression. For patients that had any two or three risk factors, the 5-year cumulative probability of progression was significantly higher (31%) compared to no risk factors (2%). Evolving iFLC >100 mg/L during follow-up was consistently associated with increased risk of progression. Based on our observations, we propose to include iFLC as a monitoring tool for all MGUS patients. Furthermore, we recommend a quarterly monitoring in all high-risk patients. Finally, we suggest that the risk of MGUS progression should be stratified with age, M-spike, and iFLC at baseline.

How we manage smoldering multiple myeloma

Smoldering myeloma (SMM) is an asymptomatic stage characterized by bone marrow plasma cells infiltration between 10-60% in absence of myeloma-defining events and organ damage. Until the revision of criteria of MM to require treatment, two main prognostic models, not overlapping each other, were proposed and used differently in Europe and in US. Novel manageable drugs, like lenalidomide and monoclonal antibodies, with high efficacy and limited toxicity, improvement in imaging and prognostication, challenge physicians to offer early treatment to highrisk SMM. Taking advantage from the debates offered by SOHO Italy, in this review we will update the evidence and consequent clinical practices in US and Europe to offer readers a uniform view of clinical approach at diagnosis, follow-up and supportive care in the SMM setting.

Treatment of Smoldering Multiple Myeloma: Ready for Prime Time?

The current standard of care for smoldering multiple myeloma (SMM) is observation until there is end-organ involvement. With newer and more effective treatments available, a question that is increasingly asked is whether early intervention in patients with SMM will alter the natural history of their disease. Herein, we review the evolving definition of SMM and risk stratification models. We discuss evidence supporting early intervention for SMM-both as a preventative strategy to delay progression and as an intensive treatment strategy with a goal of potential cure. We highlight ongoing trials and focus on better defining who may require early intervention.

Recent Advances in the Management of Smoldering Multiple Myeloma

There is remarkable progress in the treatment of multiple myeloma (MM) with significant improvement in survival in the past 10 years. Monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM) can evolve into symptomatic multiple myeloma (sy-MM) with organ involvement. SMM has associated with a much higher progression to MM compared to MGUS. In 2014, International Myeloma Working Group (IMWG) reclassified ultra-high-risk smoldering myeloma patients with bone marrow plasma cells > 60% or serum-free light chain ratio (FLCr) > 100 or > 1 focal bone lesion on the magnetic resonance imaging as MM. SMM is a heterogeneous disorder with probability for progression to myeloma up to 50% in the first 5 years. Several risk models and clinical features have been identified to stratify the risk of progression to MM. Thanks to advances in our understanding of the genomic profile of MM, there are several ongoing clinical trials, and genomic studies are being done to assess the risk of progression to MM and early intervention. There is still no standard criterion regarding when to start therapy. This review discusses identifying SMM patients who are at high risk of progression to sy-MM and recent development of new and early treatment strategies and ongoing clinical trials for these high-risk SMM patients.

Smoldering Multiple Myeloma: To Treat or Not to Treat

Smoldering multiple myeloma (SMM) is an asymptomatic, intermediate stage positioned between the plasma cell disorders of monoclonal gammopathy of undermined significance and overt multiple myeloma (MM). Although the patients with SMM have a higher risk of progression to MM in comparison to their counterparts with monoclonal gammopathy of undermined significance, their clinical course can be highly variable. The standard of care for SMM, irrespective of the risk status, continues to be observation due to paucity of high-level evidence demonstrating survival or quality-of-life benefit with early intervention. With the expanded 2014 criteria for MM utilizing biomarkers, the subset of SMM patients with 70% to 80% risk of progression at 2 years (ultra-high risk SMM) is now categorized as active MM and treated prior to the development of end-organ damage. After exclusion of this group, patients with approximately 50% risk of progression in 2 years are now considered high-risk SMM, and the value of early treatment in this subset can be established only through clinical trials. Despite its limitations, a recent phase III trial (QuiRedex) has shown survival advantage to using lenalidomide and dexamethasone doublet over observation in high-risk SMM. In this article, we review the evolving concepts in the diagnosis, risk stratification, and management of SMM.

High-risk smoldering myeloma versus early detection of multiple myeloma: Current models, goals of therapy, and clinical implications

Multiple myeloma, a bone marrow cancer, is preceded by precursor stages called monoclonal gammopathy of unknown significance and smoldering multiple myeloma. Over the past few years, highly effective and safe therapies have been made available to treat multiple myeloma. This represents a major breakthrough and has major therapeutic implications. Treatment for multiple myeloma has evolved to include treatment of precursor stages (early treatment) as these therapies are shown to be safe and effective also in smoldering myeloma. Randomized studies have shown that early treatment can delay the onset of multiple myeloma and even improve overall survival compared to observation in smoldering myeloma. The best therapeutic course and selection of patients with smoldering myeloma to treat is still a matter of debate. In this manuscript, we review the definition, management, clinical implications of smoldering myeloma and early detection of myeloma in the current context and with up-to-date data.

How We Approach Smoldering Multiple Myeloma

The Oncology Grand Rounds series is designed to place original reports published in the Journal into clinical context. A case presentation is followed by a description of diagnostic and management challenges, a review of the relevant literature, and a summary of the authors’ suggested management approaches. The goal of this series is to help readers better understand how to apply the results of key studies, including those published in Journal of Clinical Oncology, to patients seen in their own clinical practice.

Plasma cell proliferative index is an independent predictor of progression in smoldering multiple myeloma

The plasma cell proliferative index (PCPI), determined by a slide technique or by flow cytometry, detects cells in the S phase of the cell cycle and is a useful prognostic tool in patients with plasma cell disorders such as multiple myeloma and amyloidosis. We conducted a retrospective review analyzing the prognostic effect of PCPI in 306 patients with smoldering multiple myeloma (SMM). Seventy-nine (26%) patients had an elevated PCPI (>0.5). An elevated PCPI predicted an inferior time to progression (median, 3.0 vs 7.1 years for those with a low PCPI; P = .0004). Within 24 months, the progression rate was significantly higher for patients with an elevated PCPI (49% vs. 20%; P < .0001). PCPI is a valuable tool in risk stratifying patients with SMM and identifies patients with earlier progression who may benefit from closer follow-up and consideration of early intervention trials.

Association of Immune Marker Changes With Progression of Monoclonal Gammopathy of Undetermined Significance to Multiple Myeloma

IMPORTANCE

Multiple myeloma is consistently preceded by monoclonal gammopathy of undetermined significance (MGUS). Risk models that estimate the risk of progression from MGUS to multiple myeloma use data from a single time point, usually the initial workup.

OBJECTIVE

To longitudinally investigate the alterations of serum immune markers with stable vs progressive MGUS.

DESIGN, SETTING, AND PARTICIPANTS

This prospective cross-sectional cohort study included 77 469 adult participants aged 55 to 74 years in the screening arm of the National Cancer Institute Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial who had a diagnosis of progressing MGUS (n = 187) or stable MGUS (n = 498), including light-chain subtype, from November 1993, through December 2011. For each participant, all available serially stored prediagnostic serum samples (N = 3266) were obtained. Data analysis was performed from April 2018, to December 2018.

MAIN OUTCOMES AND MEASURES

Serum protein and monoclonal immunoglobulin levels, serum free light chains, and serum light chains within each immunoglobulin class were measured.

RESULTS

Of 685 individuals included in the study, 461 (67.3%) were men; the mean (SD) age was 69.1 (5.6) years. In cross-sectional modeling, risk factors associated with progressive MGUS were IgA isotype (adjusted odds ratio [OR], 1.80; 95% CI, 1.03-3.13; P = .04), 15 g/L or more monoclonal spike (adjusted OR, 23.5; 95% CI, 8.9-61.9; P < .001), skewed (<0.1 or >10) serum free light chains ratio (adjusted OR, 46.4; 95% CI, 18.4-117.0; P < .001), and severe immunoparesis (≥2 suppressed uninvolved immunoglobulins) (adjusted OR, 19.1; 95% Cl, 7.5-48.3; P < .001). Risk factors associated with progressive light-chain MGUS were skewed serum free light chains ratio (adjusted OR, 44.0; 95% CI, 14.2-136.3; P < .001) and severe immunoparesis (adjusted OR, 48.6; 95% CI, 9.5-248.2; P < .001). In longitudinal analysis of participants with serial samples prior to progression, 23 of 43 participants (53%) had high-risk MGUS before progression; 16 of these 23 (70%) experienced conversion from low-risk or intermediate-risk MGUS within 5 years. Similar results were found for light-chain MGUS.

CONCLUSIONS AND RELEVANCE

The findings of evolving risk patterns support annual blood testing and risk assessment for patients with MGUS or light-chain MGUS.

State of the science in smoldering myeloma: Should we be treating in the clinic?

Currently the standard of care for smoldering multiple myeloma (SMM) is "watch and wait." However, in recent years the treatment for multiple myeloma (MM) has shifted from cytotoxic chemotherapy with poor efficacy to less toxic, more effective treatments. Therefore, the standard for SMM is coming into question, especially for patients at the highest risk of developing MM. There are currently multiple active clinical trials investigating earlier intervention in patients with SMM. This article will review the history of SMM and how the current standard of care came to be. We will define prognostic factors of SMM and how to identify patients at highest risk of developing MM. Next we will review previous clinical trials examining treatment of SMM and finally discuss active clinical trials. While there are clear guidelines outlining management of high-risk SMM patients, they are mostly based on expert opinion and therefore it is an active area of research. Accordingly, patients should be encouraged to participate in clinical trials to better understand the benefit versus risk of early treatment.

Timing treatment for smoldering myeloma: is earlier better?

INTRODUCTION

In 2014, the International Myeloma Working Group determined that patients with ultra-high-risk smoldering multiple myeloma (SMM) should be considered for treatment as per patients with symptomatic multiple myeloma (MM), despite not having CRAB (hyperCalcemia, Renal insufficiency, Anemia, Bone disease) symptoms. Current research is elucidating whether patients with high-risk, and even intermediate-risk, SMM could benefit from early therapeutic strategies aimed at delaying progression to active MM and prolonging survival. Areas covered: The authors conducted a systematic literature search using PubMed to identify a series of patients with SMM in which prognostic and predictive factors for progression were investigated, plus the main clinical trials in SMM. Additionally, a search of active clinical trials in SMM was conducted at ClinicalTrials.gov. Expert opinion: Patients with high-risk SMM can benefit from active treatment strategies, which may prolong survival and, perhaps, provide a possible path to cure. Enabled by the limited toxicity of new drugs investigated in MM, this approach, together with consolidation with autologous transplantation, is under investigation by American and European groups. In patients with high-risk SMM who are not candidates for transplantation, combinations of oral drugs may prolong time to progression. In the near future, these approaches may be endorsed by results of ongoing clinical trials.

Monoclonal gammopathies of unknown significance and smoldering myeloma: Assessment and management of the elderly patients

Monoclonal gammopathy of unknown significance (MGUS) is the most frequent plasma cell disorder that commonly affects elderly patients. Although it is an asymptomatic condition, as well as smoldering myeloma (SMM), the risk of progression to multiple myeloma requiring therapy or other B-cell disorders varies greatly for individual patients, remaining low for MGUS (1% per year), while higher and not uniform for SMM patients (10% per year). This scenario implies some special considerations regarding assessment and follow-up, especially in the elderly. In this review, we provide the updated diagnostic criteria of monoclonal gammopathies proposed by the International Myeloma Working Group (IMGW); the current recommendations for the assessment of asymptomatic plasma cell disorders, with some concerns about the need of geriatric evaluation in the elderly population, the importance of distinguishing myeloma-related symptomatology from signs or symptoms caused by multiple chronic conditions typically found in the elderly. Finally, the identification of predictor markers of progression has enabled a proposal of risk-adapted follow-up strategies in MGUS and SMM that should be implemented in clinical practice. Although the standard of care is observation for MGUS and SMM patients as well, a recent randomized trial targeting high-risk SMM showed the clinical benefit of early intervention. The change of the treatment paradigm is also very promising and feasible for elderly patients, as long as a comprehensive geriatric assessment is conducted to optimize early treatment and reach maximum benefit with minimum toxicity, in other words, to ensure a better quality of life for these patients.

Risk stratification of smoldering multiple myeloma incorporating revised IMWG diagnostic criteria

In 2014, the International Myeloma Working Group reclassified patients with smoldering multiple myeloma (SMM) and bone marrow-plasma cell percentage (BMPC%) ≥ 60%, or serum free light chain ratio (FLCr) ≥ 100 or >1 focal lesion on magnetic resonance imaging as multiple myeloma (MM). Predictors of progression in patients currently classified as SMM are not known. We identified 421 patients with SMM, diagnosed between 2003 and 2015. The median time to progression (TTP) was 57 months (CI, 45–72). BMPC% > 20% [hazard ratio (HR): 2.28 (CI, 1.63–3.20); p < 0.0001]; M-protein > 2g/dL [HR: 1.56 (CI, 1.11–2.20); p = 0.01], and FLCr > 20 [HR: 2.13 (CI, 1.55–2.93); p < 0.0001] independently predicted shorter TTP in multivariate analysis. Age and immunoparesis were not significant. We stratified patients into three groups: low risk (none of the three risk factors; n = 143); intermediate risk (one of the three risk factors; n = 121); and high risk (≥2 of the three risk factors; n = 153). The median TTP for low-, intermediate-, and high-risk groups were 110, 68, and 29 months, respectively (p < 0.0001). BMPC% > 20%, M-protein > 2 g/dL, and FLCr > 20 at diagnosis can be used to risk stratify patients with SMM. Patients with high-risk SMM need close follow-up and are candidates for clinical trials aiming to prevent progression.

Volumetry based biomarker speed of growth: Quantifying the change of total tumor volume in whole-body magnetic resonance imaging over time improves risk stratification of smoldering multiple myeloma patients

The purpose of this study was to improve risk stratification of smoldering multiple myeloma patients, introducing new 3D-volumetry based imaging biomarkers derived from whole-body MRI.

Two-hundred twenty whole-body MRIs from 63 patients with smoldering multiple myeloma were retrospectively analyzed and all focal lesions >5mm were manually segmented for volume quantification. The imaging biomarkers total tumor volume, speed of growth (development of the total tumor volume over time), number of focal lesions, development of the number of focal lesions over time and the recent imaging biomarker ‘>1 focal lesion’ of the International Myeloma Working Group were compared, taking 2-year progression rate, sensitivity and false positive rate into account.

Speed of growth, using a cutoff of 114mm³/month, was able to isolate a high-risk group with a 2-year progression rate of 82.5%. Additionally, it showed by far the highest sensitivity in this study and in comparison to other biomarkers in the literature, detecting 63.2% of patients who progress within 2 years. Furthermore, its false positive rate (8.7%) was much lower compared to the recent imaging biomarker ‘>1 focal lesion’ of the International Myeloma Working Group.

Therefore, speed of growth is the preferable imaging biomarker for risk stratification of smoldering multiple myeloma patients.

Smoldering multiple myeloma: prevalence and current evidence guiding treatment decisions

Smoldering multiple myeloma (SMM) is an asymptomatic plasma cell proliferative disorder associated with risk of progression to symptomatic multiple myeloma (MM) or amyloidosis. In comparison to monoclonal gammopathy of undetermined significance (MGUS), SMM has a much higher risk of progression to MM. Thanks to advances in our understanding of the risk factors, the subset of patients with ultra-high risk of progression to MM (80%-90% at 2 years) has been identified. The revision of the diagnostic criteria resulted in changes in the management of this cohort of patients. In contrast to the management guidelines for MGUS patients, SMM patients need to be studied more intensively in order to identify biomarkers necessary for accurate risk stratification. In this review, we focus on the risk of progression from SMM to MM, as well as the influence of early treatment on overall survival, time to progression and quality of life.

Severe Isotype-Matched Immunosuppression (IMI) as a Potential Risk Factor for Progression of MGUS Patients

Background

Monoclonal gammopathy of undetermined significance (MGUS) precedes multiple myeloma in virtually every case. However, only a small percentage will progress and at very different rates. In addition, recent data have suggested that MGUS is associated with other comorbidities including infections, suggesting impaired immune function in some MGUS patients. Therefore, we aimed at assessing the value of isotype-matched immunosuppression (IMI; e.g., suppression of an IgAκ in an IgAλ patient), a type of immunosuppression more specific than classical immunoparesis (IP; e.g., IgG and/or IgM suppression in an IgA patient), as a prognostic marker for MGUS progression.

Methods

The Hevylite assay was used to assess IMI and immunoglobulin ratios in 307 serum samples from a cohort of 248 MGUS patients. Follow-up clinical records were available for 154 individuals.

Results

A greater incidence of IMI (51%) over classical IP (37%) was observed, although both show a progressive increase with higher risk groups. Survival analysis of 154 patients showed that severe IMI (&gt;50% suppression) differentiates 2 groups with significantly different time to progression (P = 0.024) while severe IP does not (P = 0.48). Also, a combination of severe IMI and involved monoclonal immunoglobulin &gt;1.5g/dL by Hevylite (both variables found to be independent prognostic markers in multivariate analysis) identified a group of patients with a median time to progression 6-fold shorter than the remaining group (P &lt; 0.0001).

Conclusions

These findings indicate a possible role for IMI in the malignant transformation of MGUS patients and a potential utility as a new risk factor.

Evolutionary biology of high-risk multiple myeloma

The outcomes for the majority of patients with myeloma have improved over recent decades, driven by treatment advances. However, there is a subset of patients considered to have high-risk disease who have not benefited. Understanding how high-risk disease evolves from more therapeutically tractable stages is crucial if we are to improve outcomes. This can be accomplished by identifying the genetic mechanisms and mutations driving the transition of a normal plasma cell to one with the features of the following disease stages: monoclonal gammopathy of undetermined significance, smouldering myeloma, myeloma and plasma cell leukaemia. Although myeloma initiating events are clonal, subsequent driver lesions often occur in a subclone of cells, facilitating progression by Darwinian selection processes. Understanding the co-evolution of the clones within their microenvironment will be crucial for therapeutically manipulating the process. The end stage of progression is the generation of a state associated with treatment resistance, increased proliferation, evasion of apoptosis and an ability to grow independently of the bone marrow microenvironment. In this Review, we discuss these end-stage high-risk disease states and how new information is improving our understanding of their evolutionary trajectories, how they may be diagnosed and the biological behaviour that must be addressed if they are to be treated effectively.

Smoldering Multiple Myeloma: Who and When to Treat

Smoldering multiple myeloma (SMM) is an asymptomatic plasma cell disorder characterized by the presence of ≥ 3 g/dL serum M-protein and/or 10% to 60% bone marrow plasma cell infiltration with no myeloma-defining event. The risk of progression to active multiple myeloma (MM) is not uniform, and several markers are useful for identifying patients at high risk of progression. The definition of the disease has recently been revisited and asymptomatic MMs at 80% to 90% of progression risk at 2 years are now considered to be active MM candidates for treatment. In the future, more precise biomarkers are necessary for accurate risk stratification to plan an optimized follow-up according to the risk of progression, as well as to expand the group of patients that can obtain a benefit if they receive early treatment. A phase 3, randomized trial in high-risk patients with SMM comparing early treatment versus observation has shown a significant benefit in terms of time to progression and overall survival for early intervention and confirmatory clinical trials will definitively contribute to establish the early treatment as standard of care in high-risk SMM.

Diagnosis and management of smoldering multiple myeloma: the razor's edge between clonality and cancer

Smoldering multiple myeloma (SMM) is a rare plasma cell disorder, and as the disease is asymptomatic, diagnosis is often incidental. SMM is characterized by increased marrow infiltration by clonal plasma cells and/or elevated serum M-protein in the absence of a myeloma-defining event (MDE). In recent years, SMM has gained increased attention owing to a broadening of the criteria for MDE, which include apart from the CRAB criteria, three additional parameters. Survival advantage may be offered by early treatment in the high-risk subset, based on a single trial. In this review, we assess the risk factors and models for progression to multiple myeloma. A review of our diagnostic and management approaches to SMM is presented.

Evolving changes in disease biomarkers and risk of early progression in smoldering multiple myeloma

We studied 190 patients with smoldering multiple myeloma (SMM) at our institution between 1973 and 2014. Evolving change in monoclonal protein level (eMP) was defined as ⩾10% increase in serum monoclonal protein (M) and/or immunoglobulin (Ig) (M/Ig) within the first 6 months of diagnosis (only if M-protein ⩾3 g/dl) and/or ⩾25% increase in M/Ig within the first 12 months, with a minimum required increase of 0.5 g/dl in M-protein and/or 500 mg/dl in Ig. Evolving change in hemoglobin (eHb) was defined as ⩾0.5 g/dl decrease within 12 months of diagnosis. A total of 134 patients (70.5%) progressed to MM over a median follow-up of 10.4 years. On multivariable analysis adjusting for factors known to predict for progression to MM, bone marrow plasma cells ⩾20% (odds ratio (OR)=3.37 (1.30-8.77), P=0.013), eMP (OR=8.20 (3.19-21.05), P<0.001) and eHb (OR=5.86 (2.12-16.21), P=0.001) were independent predictors of progression within 2 years of SMM diagnosis. A risk model comprising these variables was constructed, with median time to progression of 12.3, 5.1, 2.0 and 1.0 years among patients with 0-3 risk factors respectively. The 2-year progression risk was 81.5% in individuals who demonstrated both eMP and eHb, and 90.5% in those with all three risk factors.

The Changing Landscape of Smoldering Multiple Myeloma: A European Perspective

Smoldering multiple myeloma (SMM) is an asymptomatic clonal plasma cell disorder and bridges monoclonal gammopathy of undetermined significance to multiple myeloma (MM), based on higher levels of circulating monoclonal immunoglobulin and bone marrow plasmocytosis without end-organ damage. Until a Spanish study reported fewer MM-related events and better overall survival among patients with high-risk SMM treated with lenalidomide and dexamethasone, prior studies had failed to show improved survival with earlier intervention, although a reduction in skeletal-related events (without any impact on disease progression) has been described with bisphosphonate use. Risk factors have now been defined, and a subset of ultra-high-risk patients have been reclassified by the International Myeloma Working Group as MM, and thus will require optimal MM treatment, based on biomarkers that identify patients with a >80% risk of progression. The number of these redefined patients is small (∼10%), but important to unravel, because their risk of progression to overt MM is substantial (≥80% within 2 years). Patients with a high-risk cytogenetic profile are not yet considered for early treatment, because groups are heterogeneous and risk factors other than cytogenetics are deemed to weight higher. Because patients with ultra-high-risk SMM are now considered as MM and may be treated as such, concerns exist that earlier therapy may increase the risk of selecting resistant clones and induce side effects and costs. Therefore, an even more accurate identification of patients who would benefit from interventions needs to be performed, and clinical judgment and careful discussion of pros and cons of treatment initiation need to be undertaken. For the majority of SMM patients, the standard of care remains observation until development of symptomatic MM occurs, encouraging participation in ongoing and upcoming SMM/early MM clinical trials, as well as consideration of bisphosphonate use in patients with early bone loss.

Myeloma today: Disease definitions and treatment advances

There have been major advances in the diagnosis, staging, risk-stratification, and management of multiple myeloma (MM). In addition to established CRAB (hypercalcemia, renal failure, anemia, and lytic bone lesions) features, new diagnostic criteria include three new biomarkers to diagnose the disease: bone marrow clonal plasmacytosis ≥60%, serum involved/uninvolved free light chain ratio ≥100, and >1 focal lesion on magnetic resonance imaging. MM can be classified into several subtypes based on baseline cytogenetics, and prognosis varies according to underlying cytogenetic abnormalities. A Revised International Staging System has been developed which combines markers of tumor burden (albumin, beta-2 microglobulin) with markers of aggressive disease biology (high-risk cytogenetics and elevated serum lactate dehydrogenase). Although the approach to therapy remains largely the same, the treatment options at every stage of the disease have changed. Carfilzomib, pomalidomide, panobinostat, daratumumab, elotuzumab, and ixazomib have been approved for the treatment of the disease. These drugs combined with older agents such as cyclophosphamide, dexamethasone, thalidomide, bortezomib, and lenalidomide dramatically increase the repertoire of regimens available for the treatment of MM. This review provides a concise overview of recent advances in MM, including updates to diagnostic criteria, staging, risk-stratification, and management.

Future Directions in the Evaluation and Treatment of Precursor Plasma Cell Disorders

Multiple myeloma (MM) is an incurable disease that progresses from a premalignant stage termed monoclonal gammopathy of undetermined significance (MGUS) and an intermediate stage of smoldering multiple myeloma (SMM). Recent major advances in therapy with more effective and less toxic treatments have brought reconsideration of early therapeutic intervention in management of SMM, with the goal of reducing progression of the disease before the occurrence of end-organ damage to MM and improving survival. Key to this effort is accurate identification of patients at high risk of progression who would truly benefit from early intervention. In this review, we discuss the current definitions, risk factors, risk stratification, prognosis, and management of MGUS and SMM, as well as new emerging therapeutic options under active investigation.