African American patients with smoldering multiple myeloma may have a lower risk of progression compared to White patients.
Authors: Akhlaghi Theresia , Maclachlan Kylee , Korde Neha , Mailankody Sham , Lesokhin Alexander M. , Hassoun Hani , Lu Sydney X. , Patel Dhwani , Shah Urvi A , Tan Carlyn , Derkach Andriy , Lahoud Oscar Boutros , Landau Heather Jolie , Shah Gunjan L. , Scordo Michael , Chung David J. , Giralt Sergio , Usmani Saad Zafar , Landgren Carl Ola , Hultcrantz Malin 
Published: June 2022

8045 Background: The incidence of multiple myeloma (MM) is two to threefold higher in African Americans (AAs) compared to whites when adjusted for socioeconomics, age, and sex. However, there is limited information on whether racial background affects the risk of progression from smoldering MM (SMM) to MM. Methods: Patients with SMM presenting to Memorial Sloan Kettering Cancer Center between the years 2000 and 2019 and who identified as either AA or white were included in the study. Baseline characteristics were collected at the time of diagnosis including laboratory, imaging, and pathology reports. Differences in distributions of continuous and discrete characteristics were assessed by Kruskal-Wallis and chi-square tests. Time to progression (TTP) was assessed using the Kaplan-Meier method with log-rank test for comparisons. Univariate and multivariate Cox proportional hazard models were used to estimate effects of risk factors on TTP with hazard ratios (HR) and 95% confidence intervals (CI). Results: A total of 576 patients were included (70 were AA, 12%). Median follow-up time was 3 years in AAs and 4 years in whites. Differences in baseline characteristics between AAs and whites included median age (60 years in AAs vs 64 years in whites, p = 0.01), median hemoglobin level (12.3g/dL in AA vs 12.8g/dL in whites, p = 0.02), and immunoparesis including 1 or 2 uninvolved immunoglobulins (31% and 10% in AAs vs 56% and 27% in whites, p = 0.002). There was no difference in bone marrow plasma cells, M-spike, free light chain ratio, or Mayo-2018 SMM risk score. AA race was associated with a significantly decreased risk of progression in the univariate model (HR 0.57, CI 0.34-0.94). In the multivariate model adjusting for age, sex, and variables associated with an increased risk of progression in the univariate model (bone marrow plasma cells, M-spike, free light chain ratio, immunoparesis and low albumin), AA race remained associated with a decreased risk of progression (HR 0.39, CI 0.16-0.95). Overall, AA patients with SMM had a significantly (p = 0.027) longer median TTP (9.7 vs 6.2 years), and a lower 2-year (12.6% vs 20.1%) and 5-year (34% vs 44.6%) progression rate than whites. Because AA patients were younger at diagnosis, we stratified patients by age group, < 65 vs ≥65 years. In patients < 65 years, there was no difference in progression rate. In patients aged ≥65 years, AA patients continued to have a longer TTP than whites (9.8 vs 5.2 years, p = 0.02). Conclusions: In our retrospective single institution experience, AA patients with SMM had a lower risk of progression to MM compared to whites. Both groups had similar Mayo-2018 risk scores, however, AA patients had a lower degree of immunoparesis at baseline. Future studies are needed to better understand if these differences are explained by differences in disease biology including genomic mechanisms, immune microenvironment, and systemic immune response.