Influence of Rurality, Race, and Ethnicity on Non-Hodgkin Lymphoma Incidence

Introduction: Exposure to lymphomagens vary by geography. The extent to which these contribute to racial and ethnic disparities in non-Hodgkin lymphoma (NHL) incidence is not well understood. We sought to evaluate the association between urban–rural status and racial and ethnic disparities in the 3 major NHL subtypes: diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), and chronic lymphocytic leukemia (CLL). Patients and Methods: We used data on NHL incidence from 21 Surveillance, Epidemiology, and End Results (SEER) population-based registries for the period 2000 to 2016. Population characteristics were compared by NHL subtype and urban–rural status, using rural-urban continuum codes from the US Department of Agriculture. Incidence rate ratios were calculated, and Poisson regression was used to assess the association between incidence and rurality. Results: A total of 136,197 DLBCL, 70,882 FL, and 120,319 CLL incident cases aged ≥ 20 years were reported. The majority of DLBCL patients were non-Hispanic white (73.5%), with 11.9% Hispanic and 7.3% non-Hispanic black, with a similar distribution observed in FL and CLL. Adjusting for age, sex, and family poverty, we found increased DLBCL incidence among Hispanics in increasingly urban areas compared to rural areas (rural incidence rate ratio [IRR] = 1.00; nonmetropolitan urban IRR = 1.32, 95% CI 1.16, 1.51; metropolitan urban IRR = 1.55, 95% CI 1.36, 1.76). Among non-Hispanic blacks, urban areas, relative to rural areas, were associated with increased CLL incidence (IRR = 1.48; 95% CI 1.27, 1.72). Conclusion: Urban–rural incidence patterns suggest that environmental exposures in urban areas associated with DLBCL and CLL pathogenesis may disproportionately affect Hispanics and non-Hispanic blacks. Urban–rural incidence patterns may help clarify underlying racial and ethnic disparities in non-Hodgkin lymphoma (NHL) incidence. In our large study using national Surveillance, Epidemiology, and End Results (SEER) data, we found that urban status was associated with increased incidence of diffuse large B-cell lymphoma in Hispanics and chronic lymphocytic leukemia in non-Hispanic blacks, suggesting a potential differential NHL risk among diverse, urban populations.