Background: Monoclonal gammopathy of undetermined significance (MGUS) is the precursor to multiple myeloma (MM). MM disproportionately affects black individuals, but the cumulative risk of progression from MGUS to malignancy does not differ by race. Hence, the racial disparities in MM incidence appear to arise from differences in the occurrence of MGUS. Nonetheless, MGUS has been studied mainly in white populations; the study that first described the natural history of MGUS was conducted by Kyle, et al. (2006) in 97.3% white Olmsted County, Minnesota. Methods: We determined the prevalence of MGUS among black South African men >30 years of age at the Chris Hani Baragwanath Academic Hospital in Johannesburg. We conducted serum protein electrophoresis (SPEP) and free light chain (FLC) quantification and used the same criteria for MGUS as the Olmsted County studies: a monoclonal protein on SPEP or an abnormal FLC-ratio plus elevation in the appropriate FLC. We also investigated the association between MGUS and various clinical and behavioral factors. Results: The prevalence of MGUS in our cohort (n=386) was 8.03% (95%CI 5.32-10.74), nearly 1.6-fold higher than in Olmsted County males. In a univariable logistic regression model, MGUS was associated with HIV status (odds ratio (OR) 2.39, 95%CI 0.95-5.51), but in the adjusted model that also included body mass index (BMI) and cigarette use, the magnitude of the association decreased to an OR of 2.17 and was not statistically significant. MGUS was associated with current (vs. never) cigarette smoking in both univariable (OR 5.2, 95%CI 1.53-24.0) and multivariable (OR 4.11, 95%CI 1.08-20.4) models. Conclusions: Not only did we find the prevalence of MGUS in black South African men to be substantially higher than in white populations, but we also report that MGUS cases are associated with potentially modifiable risk factors. Building on this pilot study, a larger study is currently underway powered to confirm the relationship between MGUS and HIV, as well as between MGUS and cigarette smoking, in a black African population inclusive of both genders. Future studies designed to evaluate genetic and matched-environmental contributions may elucidate racial disparities and facilitate the development of strategies to prevent plasma cell malignancies.

*Covariates with p<0.15 were included in the multivariable model.