Monoclonal Protein Concentration and Risk of Multiple Myeloma: Is 0.5 g/DL the New 1.5?

Introduction: Monoclonal Gammopathy of Undetermined Significance (MGUS) is an asymptomatic clonal plasma cell disorder with a risk of progression to multiple myeloma (MM). To provide an accurate prognosis, monoclonal protein (M-protein) concentration has been used to assess risk of progression to myeloma. Current risk models developed from stored serum samples in a predominately white population of patients indicated a low risk of progression (less than 1% per year) in patients with M-protein of <1.5 g/dL. Little is known about M-protein concentration and risk of progression in patients tested during routine clinical care in a more diverse population. We assessed the outcomes of MGUS five years after diagnosis, and determined the association between baseline characteristics and the rate of progression to MM.

Methods: We used data from national Veterans Health Administration system to identify patients diagnosed with MGUS from 1999-2021 and were followed from MGUS diagnosis until progression, death, or the date 7/11/2023 was reached. MGUS diagnosis and progression to MM was confirmed utilizing a natural language processing algorithm. We included patients of black and white race and those with IgG, IgA, or light chain MGUS. The exposure was M-protein concentration at MGUS diagnosis, stratified by ≤0.5, >0.5-≤1.0, >1.0-≤1.5, >1.5 g/dL. We plotted the cumulative incidence function curve and used a multivariable Fine-Gray sub distribution hazard model with progression at 5 years as the event of interest, and death as a competing event. Covariates included sex, race, MGUS type, age, body mass index (BMI), diabetes, renal disease, and other comorbidities summarized by Charlson Comorbidity Index at MGUS diagnosis.

Results: We included 15,520 patients with MGUS. The mean age at the diagnosis was 71.1. IgG subtype was more common (83.2%) than IgA (12.7%), and light chain (4.1%). 19.6% and 39.5% of patients had renal disease and diabetes, respectively. Black veterans represented 5600 (36.1%) of the cohort. At 5 years, 26.6% of veterans with an M-protein of >1.5 g/dL were diagnosed with myeloma, compared to 11.7% with 1.1-1.5 g/dL, 6.9% with 0.6-1.0 g/dL, and 3.3% with ≤0.5 g/dL. In multivariable models an M-protein >1.5 was associated with a greater risk of progression compared to ≤0.5 (multivariable-adjusted Hazard Ratio [aHR] 9.76, 95% Confidence Interval [CI] 8.37-11.40). Overall, increasing age was shown to have lower risk of transitioning to MM at 5 years with aHR of 0.983 (95% CI 0.978-0.988).

Conclusion: In this modern cohort, only an M-protein of ≤0.5 g/dL was associated with a less 1% per year risk of developing MM. Conversely, 26.6% of veterans with an M-protein level >1.5 g/dL developed MM at 5 years. Risk of MM in patients clinically evaluated for MGUS may be higher than previously thought and new models of MM progression should be developed.