Environmental Cadmium Exposure and Odds of Residing in a Breast Cancer Hotspot in Kentucky

BACKGROUND AND AIM: Breast cancer is the most common invasive cancer diagnosed in US women. Cadmium is a carcinogenic heavy metal pollutant found in cigarettes and as an agricultural and industrial byproduct. Studies of cadmium exposure and breast cancer risk have produced mixed results depending upon methodology. We examined environmental cadmium exposure and risk of residing in a breast cancer hotspot in Kentucky. METHODS: Invasive breast cancer cases diagnosed between 1995-2018 were identified from the Kentucky Cancer Registry (n=66,413) and 68 of the 1,114 KY census-tracts were identified as breast cancer clusters using Getis-Ord Gi* for age-standardized rates. Census-tract cadmium concentrations from the 2014 National Air Toxics Assessment interpolated estimations were linked to cases’ residential addresses. Logistic regression was performed to assess the odds of residing in a hotspot across quartiles of cadmium exposure adjusted for individual-level (demographic, reproductive factors, Appalachian residence, insurance, tobacco use) and neighborhood factors (population density, poverty, and physical inactivity). Effect modification by smoking was assessed. RESULTS:4,134 women with breast cancer resided in hotspots (6.2%), which were located in major cities and southeast Kentucky. The mean age was 61 years. Hotspot cases were more likely than other cases to be black, single, uninsured or have public insurance, live in Appalachia, and reside in more densely populated neighborhoods with greater poverty. The odds of living in a hotspot were 4.2-times higher for those who resided in areas with the highest quartile of cadmium exposure compared to those in the lowest (95% CI: 3.6, 4.8; p-trend 0.0001). Results were similar (Q4 vs Q1: OR=4.4 95% CI 3.6, 5.4) among non-smokers. CONCLUSIONS:The observed associations of environmental cadmium exposure and residing in breast cancer hotspots in Kentucky warrant further research with more appropriate epidemiologic study designs. KEYWORDS: heavy metals, cancer and cancer precursors, environmental epidemiology, female, hotspot, air pollution