Diagnosis and management of smouldering myeloma: A British Society for Haematology Good Practice Paper

Multiple myeloma is a bone marrow-based plasma cell tumour that develops from asymptomatic pre-cursor conditions smouldering myeloma and monoclonal gammopathy of uncertain significance and all are characterised by the presence of a monoclonal protein in the blood. Diagnosis and distinction between these conditions is based on blood tests, the bone marrow biopsy and cross sectional imaging. There are various risk stratification models that group patients with smouldering myeloma into risk groups based on risk of progression to symptomatic disease. Management is mainly observational for patients with smouldering myeloma although clinical trials for high-risk disease may be available. Restaging is required if evidence for 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.

Smoldering multiple myeloma: evolving diagnostic criteria and treatment strategies

The adage for smoldering myeloma (SMM) has been to observe without treatment, until criteria for active multiple myeloma were satisfied. Definitions and risk stratification models have become more sophisticated, with prognostication tailored to include high-risk cytogenetics as per the most recent International Myeloma Working Group 2020 risk model. Moreover, progress in defining genomic evolution and changes in the bone marrow microenvironment through the monoclonal continuum have given insight into the complexities underlying the different patterns of progression observed in SMM. Given recent data showing improved progression-free survival with early intervention in high-risk SMM, the current dilemma is focused on how these patients should be treated. This case-based article maps the significant advancements made in the diagnosis and risk stratification of SMM. Data from landmark clinical trials will also be discussed, and ongoing trials are summarized. Ultimately, we outline our approach to SMM and hope to impart to the reader a sound concept of the current clinical management of SMM.

Daratumumab monotherapy for patients with intermediate-risk or high-risk smoldering multiple myeloma: a randomized, open-label, multicenter, phase 2 study (CENTAURUS)

Current guidelines for smoldering multiple myeloma (SMM) recommend active monitoring until the onset of multiple myeloma (MM) before initiating treatment or enrollment in a clinical trial. Earlier intervention may delay progression to MM. In CENTAURUS, 123 patients with intermediate-risk or high-risk SMM were randomly assigned to daratumumab 16 mg/kg intravenously on extended intense (intense), extended intermediate (intermediate), or short dosing schedules. At the prespecified primary analysis (15.8-month median follow-up), the complete response (CR) rates (co-primary endpoint) were 2.4%, 4.9%, and 0% for intense, intermediate, and short dosing, respectively; the co-primary endpoint of CR rate >15% was not met. Progressive disease (PD)/death rates (number of patients who progressed or died divided by total duration of progression-free survival [PFS] in patient-years; co-primary endpoint) for intense, intermediate, and short dosing were 0.055 (80% confidence interval [CI], 0.014-0.096), 0.102 (80% CI, 0.044-0.160), and 0.206 (80% CI, 0.118-0.295), respectively, translating to a median PFS ≥24 months in all arms (P < 0.0001, <0.0001, and =0.0213, respectively). With longer follow-up (median follow-up, 25.9 months), CR rates were 4.9%, 9.8%, and 0% for intense, intermediate, and short dosing, respectively. PD/death rates for intense, intermediate, and short dosing were 0.059 (80% CI, 0.025-0.092), 0.107 (80% CI, 0.058-0.155), and 0.150 (80% CI, 0.089-0.211), respectively, again translating to a median PFS ≥ 24 months in all arms (P < 0.0001 for all arms). Twenty-four-month PFS rates were 89.9% (90% CI, 78.5-95.4%), 82.0% (90% CI, 69.0-89.9%), and 75.3% (90% CI, 61.1-85.0%) for intense, intermediate, and short dosing, respectively. Pharmacokinetic analyses indicated that intense dosing maintained target-saturating trough concentrations in most patients throughout weekly, every-2-week, and every-4-week dosing periods. No new safety signals were observed. These data provide the basis for an ongoing phase 3 study of daratumumab in 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.

Current and potential applications of positron emission tomography for multiple myeloma and plasma cell disorders

Fluorine-18 (18F)-fluorodeoxyglucose (FDG) positron emission tomography (PET) allows evaluation of elevated glucose metabolism in malignancies. There has been increasing interest in FDG PET/CT for plasma cell disorders since the International Myeloma Working Group outlined multiple applications of this imaging modality, including distinguishing smoldering myeloma from active multiple myeloma, confirmation of solitary plasmacytoma, and multiple indications in patients with known multiple myeloma, including determining extent of initial disease, monitoring therapy response, and detection of residual disease following therapy. The field of molecular imaging is now shifting focus from evaluation of metabolism to targeted evaluation of specific tumor markers. Targeted PET imaging targeted of CXCR4 and CD38 has advanced into translational clinical trials, bringing us closer to powerful imaging options for myeloma. In this review we discuss the current applications of FDG PET/CT in plasma cell disorders, as well as advances in targeted PET imaging.

Necrobiotic xanthogranuloma associated with smoldering multiple myeloma: satisfactory response to cyclophosphamide, dexamethasone, and thalidomide

Necrobiotic xanthogranuloma is a rare chronic condition, belonging to the group C non-Langerhans cell histiocytoses, which is relevant due to the possibility of extracutaneous involvement and association with systemic diseases, particularly hematologic malignancies. The case reported here was only diagnosed after nine years of evolution and was associated with plasma cell dyscrasia. After treatment with cyclophosphamide, dexamethasone, and thalidomide, there was a reduction of cutaneous lesions and serum levels of monoclonal protein.

Genomic patterns of progression in smoldering multiple myeloma

We analyzed whole genomes of unique paired samples from smoldering multiple myeloma (SMM) patients progressing to multiple myeloma (MM). We report that the genomic landscape, including mutational profile and structural rearrangements at the smoldering stage is very similar to MM. Paired sample analysis shows two different patterns of progression: a "static progression model", where the subclonal architecture is retained as the disease progressed to MM suggesting that progression solely reflects the time needed to accumulate a sufficient disease burden; and a "spontaneous evolution model", where a change in the subclonal composition is observed. We also observe that activation-induced cytidine deaminase plays a major role in shaping the mutational landscape of early subclinical phases, while progression is driven by APOBEC cytidine deaminases. These results provide a unique insight into myelomagenesis with potential implications for the definition of smoldering disease and timing of treatment initiation.