The incidence of the most common form of liver cancer (75-85%), hepatocellular carcinoma (HCC), has increased since the 1970s. Internationally, liver cancer is the second most common cause of cancer-related death. HCC risk factors can include chronic hepatitis B and C virus infection, excessive alcohol consumption, aflatoxin exposure, tobacco use, and nonalcoholic fatty liver disease (NAFLD). Recent studies suggest that the incidence of HCC could be influenced by environmental exposures due to liver cancer’s geographic variation. Dioxin and dioxin-like compounds can be found in environmentally toxic emissions that could have adverse effects on the locally exposed human population. Dioxins and dioxin-like compounds include persistent organic pollutants [e.g., polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs)] that are produced from industrial combustion processes including waste incineration. These environmental exposures can be harmful to humans through the consumption of meat from animals that ingest them, inhalation, and dermal absorption. Various types of industrial facilities can release these pollutants: municipal solid waste, medical waste, and other types of incinerators as well as secondary copper smelters. These pollutants can also be found in the soil proximate to and residential dust from homes near the industrial facilities. There are few population-based studies of environmental exposures to ambient dioxin emissions and liver cancer. To address this research gap, the VoPham group in the Public Health Sciences Division examined the association between county-level ambient dioxin air emissions from industrial sources and incidence rates of HCC in the general US population. This study was published in Environmental Research.
Summarizing the results, Dr. Trang VoPham said, “this study showed that higher levels of dioxin emissions from industrial sources, based on the number of dioxin-emitting facilities within a county or average annual emissions within a county, was not associated with the risk of developing HCC. However, in analyses by dioxin facility type, there were some signals of positive associations between county-level dioxin emissions from coal-fired power plants, industrial boilers, and sewage sludge incinerators and HCC risk – although results were not consistent across both exposure metrics.”
This study contributes to the existing literature, going beyond occupational exposures and accidental contamination via air emissions from industrial sources. Other strengths of this study included “linking two large nationwide databases to conduct this study – (1) a spatial database of geocoded dioxin-emitting facilities (which included information from the US Environmental Protection Agency (EPA) and hospital locations from Esri with presumed medical waste incinerators) and (2) the National Cancer Institute (NCI) Surveillance, Epidemiology, and End Results (SEER) database (with information on HCC cases from population-based cancer registries across the US). This data linkage was performed using a geographic information system (GIS) to combine location-based information available from both databases”, stated Dr VoPham.
Dr. VoPham concluded, “the findings from this hypothesis-generating study warrant further investigation to understand how dioxin emissions might impact the risk of developing HCC. Future research could improve on the limitations of this study, which included an ecological study design based on the county. Further, it will be important for future research to use individual-level data to improve the exposure assessment and adjustment for confounding.”
This research was supported by the National Institutes of Health (NIH), National Institute of Diabetes and Digestive and Kidney Disease (NIDDK) (K01 DK125612), and the Intramural Research Program of the National Cancer Institute (NCI).
Fred Hutch/UW Cancer Consortium member Trang VoPham contributed to this work.
VoPham T, Bertrand KA, Fisher JA, Ward MH, Laden F, Jones RR. Emissions of dioxins and dioxin-like compounds and incidence of hepatocellular carcinoma in the United States. Environmental Research. 2022 Mar 1;204:112386.