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County‐level cumulative environmental quality associated with cancer incidence
Jagai, J., L. Messer, K. Rappazzo, C. Gray, S. Grabich, AND D. Lobdell. County‐level cumulative environmental quality associated with cancer incidence. Cancer. John Wiley & Sons Incorporated, New York, NY, 123(15):2901-2908, (2017).
In this study we use the Environmental Quality Index (EQI) to investigate associations between cancer incidence and simultaneous environmental exposures. Individual environmental exposures have been associated with cancer development; however, a variety of environmental exposures may occur simultaneously. The EQI is a county-level measure of cumulative environmental exposures, occurring in five domains, representing the time period 2000-2005. The EQI was used to assess associations between cumulative environmental exposures and cancer incidence. Because the overall environment, as represented by the EQI, is comprised of measures that may influence health in a negative, neutral, or positive manner, and we wish to better understand the complex relationships between environmental quality and health, we also examine associations between domain indices. This study takes the focus from single harmful environmental exposures to a broader view of the environment encompassing several domains, and provides context for further studies of cancer incidence and the broad environment.
Background: Cancer risk is affected by a combination of behavioral, genetic, and environmental factors. Individual environmental exposures have been associated with cancer development; however, a variety of environmental exposures may occur simultaneously. The Environmental Quality Index (EQI) is a county-level measure of cumulative environmental exposures, occurring in five domains, representing the time period 2000-2005. The EQI was used to assess associations between cumulative environmental exposures and cancer incidence. Methods: The EQI was linked to county-level annual age-adjusted cancer incidence rates for 2006-2010 from the Surveillance, Epidemiology, and End Results (SEER) Program state cancer profiles. All-site cancer and the top three site-specific cancers for males and females were considered. We estimated incident rate differences (IRD) and 95% confidence intervals (CI) using fixed-slope, random intercept multi-level linear regression models. Associations were assessed with domain-specific indices (air, water, land, built, and sociodemographic) and all analyses were stratified by rural-urban status.Results: Comparing the highest quintile/poorest environmental quality to the lowest quintile/best environmental quality for the overall EQI, the all-site county-level cancer incidence rate was strongly positively associated with poor environmental quality overall (IRD: 38.55, 95%CI 29.57,47.53) and for both males (IRD: 32.60, 95%CI 16.28,48.91) and females (IRD: 30.34, 95%CI 20.47,40.21), indicating a potential increase in cancer incidence with decreasing environmental quality. Rural-urban stratified models demonstrated strong associations comparing highest to the lowest quintiles for all strata, except the thinly populated/rural stratum and in the metropolitan-urbanized strata, demonstrating increasingly poor environmental quality was associated with increasing cancer rates. When considering site-specific cancers, prostate and breast cancer demonstrated the strongest associations with poor environmental quality.Conclusion: We observed strong positive associations between the EQI and all-site cancer incidence rates. Associations differed by rural-urban status and by the five environmental domains considered. The most urbanized areas had the strongest associations for both males and females and across the domain-specific indices. These results suggest that overall environmental quality can influence cancer risk and that associations vary by urbanicity. This study demonstrates that research focusing on single environmental exposures in cancer development may not address the broader environmental context in which cancers develop and future research needs to consider cumulative environmental exposures.