Investigation of the role of environmental polycyclic aromatic hydrocarbon endocrine disrupting chemicals in breast cancer

Cancers are a complex set of related diseases with wide ranging etiologies, and humans are exposed to a milieu of environmental exposures that may contribute to disease development. Breast cancer in particular is a complex and multifactorial disease, yet prior research has largely focused on studying exposures to one factor/contaminant at a time, which does not reflect the real-world environment. In addition, investigating incidence of total breast cancer has the potential to mask the impacts of environmental factors on 1) the development of different subsets of breast cancer, varying in hormone receptor status and 2) progression of these cancers to advanced and more aggressive stages. Patients with distant metastatic breast cancer have poor prognosis despite aggressive, multidisciplinary treatment regimens compared to carcinoma in situ or early-stage breast cancer. This reinforces the unmet need to identify risk factors associated with advanced breast cancers to reduce incidence and improve overall breast cancer outcomes. The objective of these studies was thus to determine environmental risk factor associations with breast cancer by stage, and to utilize a real world environmental exposure chemical mixture to interrogate potential impacts on breast tumor progression by hormone receptor status.

These studies begin by evaluating the associations between breast cancer summary stages and the Environmental Quality Index (EQI), which includes a range of environmental factors across five overarching environmental domains. Our analysis found total and localized breast cancer incidence were increased in counties with poor environmental quality compared to those with good environmental quality. These overall environmental trends were largely driven by land quality, which was associated with incidence of early-stage disease (carcinoma in situ and localized breast cancer), in addition to total breast cancer, especially in urban counties.

Taking advantage of more granular patient data, these studies further evaluated the odds of localized, regional, or distant metastatic breast cancer in categories of environmental quality using women with carcinoma in situ as registry-based controls. Overall environmental quality was not associated with invasive breast cancer; however, poor land environmental quality was associated with increased odds of all invasive breast cancer types, particularly in more rural communities (distant metastatic breast cancer was 5-8% more likely compared to carcinoma in situ). Cumulatively, epidemiologic analyses indicate significant associations between poor overall and land environmental quality and breast cancer incidence as well as odds of invasive breast cancer. Furthermore, associations differed by breast cancer summary stage, rural-urban status, and environmental domain thus identifying a critical need to assess cumulative environmental exposures in the context of cancer stage.

Emerging evidence suggests the role of environmental chemicals, in particular endocrine disrupting chemicals (EDCs), in incidence and progression of breast cancer, which can impact survival outcomes. Polycyclic aromatic hydrocarbons (PAHs) are a toxic and ubiquitous class of environmental chemicals, many of which exhibit endocrine disrupting activity. They are products of fuel combustion from human and natural sources. PAH exposure is widespread, and many PAHs are considered carcinogenic. Urinary metabolite data were collected from 9517 individuals from the U.S. CDC National Health and Nutrition Examination Survey years 2005-2014 for four parental PAHs naphthalene, fluorene, phenanthrene, and pyrene. We utilized these urinary biomarkers to estimate PAH intake, and regression models were fit for multiple demographic and lifestyle variables, to determine variable effects, interactions, odds of high versus low PAH intake. Smoking and secondhand smoke (SHS) exposure accounted for the largest PAH intake rate variability (25.62%), and there were strongest interactions between race and ethnicity and smoking or secondhand smoke exposure, reflected in a much greater contribution of smoking to PAH intake in non-Hispanic Whites as compared to other racial and ethnic groups. Increased risk of high PAH intake was observed in older age groups, obese persons, college graduates, midrange incomes, smokers, and those who were SHS exposed. Among the non-smoking population, effects of other demographic factors lessened, suggesting a highly interactive nature. Results suggest that there are demographic subpopulations with high PAH intake because of different smoking behaviors and other exposures.

The PAH-contaminated Atlantic Wood Industries, Inc. (AWI) Superfund site in Portsmouth, Virginia provides a model for studying a real-world complex PAH mixture, and its extrapolation to cancer risk and PAH exposure in the general population. Cancer risk at the Superfund site due to sediment-derived PAHs was examined and PAH sources in the general population upon PAH mixture exposure were then evaluated. The PAH mixture was assessed for potential carcinogenicity using US EPA’s OncoLogic ranking tool and the US EPA list of priority PAHs. Cancer risk due to PAH exposure was calculated for Superfund site users and compared to the US EPA assessment. Human intake and health endpoints of PAHs within the mixture were extracted from USEtox chemical fate database. Eleven PAH compounds within the mixture were of carcinogenic concern, and seven PAHs conveyed significant excess cancer risk at the Superfund site and in the general population, wherein PAH-contaminated seafood ingestion was a main route of exposure.

Most research tends to focus on tumor etiology and the effect of single chemicals, offering little insight into the effects of realistic complex mixture exposures on tumor progression. To address this issue, the final portion of this work investigated the effect of the previously mentioned AWI Superfund site-derived PAH-enriched EDC mixture in a panel of normal mammary epithelial cells and breast cancer cell models. Cells or organoids in culture were treated with EDC mixture at doses estimated from U.S. adult intake of the top four PAH compounds within the mixture from the National Health and Nutrition Examination Survey database. Physiologic doses of this PAH mixture (6, 30, 300nM) demonstrated increased aryl hydrocarbon receptor (AhR) expression and CYP activity in estrogen receptor (ER) positive, but not normal mammary epithelial cells or ER negative breast cancer cells. In addition, upregulated AhR signaling corresponded with increased cell proliferation and expression of anti-apoptotic and antioxidant proteins XIAP and SOD1. A mathematical model was employed to validate PAH-mediated increases in AhR and XIAP expression in the MCF-7 ER-positive cell line. Furthermore, the PAH mixture caused significant growth increases in ER-negative breast cancer cell derived 3D tumor organoids, providing further evidence for the role of a real world-derived PAH mixture in enhancing a tumor proliferative phenotype.

Results from these studies have implications for cancer control and prevention and targeted PAH exposure reduction initiatives by identifying vulnerable subpopulations, and further identify key consequences of PAH exposure and how it may contribute to breast cancer biology and progression.