Risk of monoclonal gammopathy of undetermined significance (MGUS) and subsequent multiple myeloma among African American and white veterans in the United States.

The age-adjusted incidence of multiple myeloma (MM) is 2-fold higher in African Americans than in whites. A few small studies have reported a higher prevalence of monoclonal gammopathy of undetermined significance (MGUS) in African Americans versus whites. Etiologic factors for MGUS and determinants for transformation of MGUS to MM are unknown. We quantified the prevalence of MGUS and subsequent risk of MM among 4 million African American and white male veterans admitted to Veterans Affairs (VA) hospitals. The age-adjusted prevalence ratio of MGUS in African Americans compared with whites was 3.0 (2.7-3.3 95% confidence interval). Among 2046 MGUS cases, the estimated cumulative risk of MM during the first 10 years of follow-up was similar (P = .37) for African Americans (17%) and whites (15%). In the largest study to date, we suggest that the excess risk of MM in African Americans results from an increase in risk of MGUS rather than an increased risk of progression from MGUS to MM.