SUMMARY: Multiple Myeloma (MM) is a clonal disorder of plasma cells in the bone marrow. It evolves from a precursor stage called Monoclonal Gammopathy of Unknown Significance (MGUS) to MM. Smoldering Multiple Myeloma (SMM) is an intermediate stage in this process of disease evolution. The risk of MGUS transforming into MM is approximately 1% per year. Smoldering Multiple Myeloma or asymptomatic MM is a precursor to MM and is characterized by at least 10% plasma cells in the bone marrow or M-spike of at least 3 g/dl, or both, but these patients have no evidence of active symptomatic Myeloma with associated end-organ damage such as hypercalcemia, renal insufficiency, anemia or bone lesions. Even though only 10% of patients with SMM progress to MM annually, over 50% of the SMM patients with high risk features will progress to MM in the first 2 years.
The current recommendations for those with SMM are periodic monitoring and treatment intervention only when disease progresses to MM. SMM patients with high risk features include those with at least 10% plasma cells in the bone marrow, a Monoclonal component (IgG monoclonal spike of at least 3 g/dL, IgA M-spike of at least 2 g/dL or a urinary Bence Jones protein level of more than 1 g per 24 hours) or only one of the above two criteria plus at least 95% abnormal plasma cells in the bone marrow, with a reciprocal decrease in one or two uninvolved immunoglobulins of more than 25%, compared to normal values.
Identifying SMM patients who are at a high risk for progression to Multiple Myeloma can allow for early intervention to prevent end-organ damage and potentially achieve long-term remission. Current prognostic models rely solely on clinical markers and do not fully capture the risk of SMM progression. The authors in this study hypothesized that genetic alterations can predict the risk of progression from SMM to overt Multiple Myeloma (MM).
The researchers conducted a multicenter study on bone marrow samples from 214 patients at the time of diagnosis with SMM, using Next-Generation Sequencing (NGS) technologies. This study included an external validation cohort of 72 patients with SMM, whose tumor DNA has been previously sequenced. Whole-Exome Sequencing was performed on 166 tumor samples, and deep targeted sequencing on 48 tumor samples. This study excluded patients who presented at diagnosis with MM related findings such as hypercalcemia, renal impairment, anemia, or bone lytic lesions or who had any myeloma-defining event. Patients with light-chain and nonsecretory SMM were however included. The median patient age was 62 years. Patients were followed up for a median of 6.8 years to identify which of these patients developed myeloma, and the researchers then cross-linked the molecular and clinical data to explore whether certain genomic abnormalities increased the risk of progression to myeloma.
It was noted that most of the genetic alterations necessary for progression to MM were already present by the time of diagnosis of SMM and were all independent risk factors of progression, after accounting for clinical risk staging. They included alterations of the MAPK pathway (KRAS and NRAS Single Nucleotide Variants-SNVs), DNA repair pathway (deletion 17p, TP53, and ATM SNVs) and amplification or translocation of MYC gene.
Patients who harbored MYC aberrations (translocations or amplifications) had the shortest median Time to Progression (8.4 versus 51.6 months; P<0.001) followed by those with MAPK pathway mutations (14.4 versus 60 months; P<0.001) and DNA repair pathway alterations (15.6 versus 50.4 months; P=0.004). These findings were validated in the external cohort of 72 patients with SMM whose tumor DNA had been previously sequenced and the researchers found that patients with any of the high-risk genetic alterations also had a higher risk of progression to MM. APOBEC (“apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like”) associated mutations were enriched in patients who progressed to MM, and were associated with a shorter time to progression.
It was concluded that the genetic alterations with Smoldering Multiple Myeloma are essentially the same as full-fledged myeloma suggesting that by the time Smoldering Multiple Myeloma is diagnosed, most of the molecular abnormalities found in myeloma have already occurred. The authors added that genomic predictors of progression could identify patients at high risk of progression to Multiple Myeloma and thus improve on the precision of current clinical models. However, the role played by tumor microenvironment in the risk of disease progression, remains to be determined.
Genomic Profiling of Smoldering Multiple Myeloma Identifies Patients at a High Risk of Disease Progression. Bustoros M, Sklavenitis-Pistofidis, Park J, et al. J Clin Oncol 2020;38:2380-2389.