Abstract 2304: Environmental pollutants and breast cancer: 2006-2016 epidemiological studies designed to evaluate biological hypotheses provide evidence of risk for certain pesticides, organic solvents, and products of combustion

Common environmental chemicals have plausible links to breast cancer because they are mammary gland carcinogens in animal studies or are known to activate relevant hormonal pathways or enhance susceptibility of the mammary gland to carcinogenesis. An institute of Medicine report prioritized human studies of these exposures. Yet the long latency and multifactorial etiology of breast cancer make evaluation of these chemicals in humans challenging, adding to the importance of study designs that are well-suited to capture hypothesized breast-cancer mechanisms. With this in mind, we updated Brody et al’s 2007 review in Cancer to evaluate the strength of the epidemiologic evidence for several classes of chemicals with widespread exposure. We conducted a systematic search of the PubMed database for articles published in 2006-2016 using 147 terms and the inclusion/exclusion criteria defined in Brody et al’s 2007 review. We critically reviewed articles identified by our search, including whether study designs were suited to the biological evidence. We identified 158 new articles since 2006. In the past 10 years, the strength of evidence for an association between breast cancer and banned but persistent endocrine disrupting chemicals polychlorinated biphenyls (PCBs) and organochlorine pesticides has increased, based on a unique 50-year cohort study that captured exposure during potentially critical windows for breast development (in utero, adolescence, pregnancy) and at the time when the chemicals were still in use. Studies that considered early life exposure to organic solvents and/or exposure of long duration also added to evidence for an association with breast cancer. Solvents are used in dry cleaning, electronics manufacturing, leather and fur processing, and metal, auto, textile, and some military work. Other important reports included the U.S. Agricultural Health Study, which provided the first evidence of an association between organophosphate pesticides and breast cancer. Analyses from the Long Island Breast Cancer Study Project showed higher risk associated with polycyclic aromatic hydrocarbons (PAHs, products of combustion) in women with certain genetic variations. Consumer product chemicals, including BPA, phthalates, per fluorinated compounds, and hair dyes were evaluated in a few studies with inconsistent results; many of these studies had serious methodologic limitations. Animal and mechanistic evidence suggest that timing could be crucial to carcinogenic actions of many environmental chemicals, however we found that most epidemiologic studies in the past 10 years did not evaluate a specific timeframe of exposure prior to diagnosis. Those that did enhanced our understanding of relevant windows for biological activity of certain classes of chemicals. Citation Format: Kathryn M. Rodgers, Julia O. Udesky, Ruthann A. Rudel, Julia G. Brody. Environmental pollutants and breast cancer: 2006-2016 epidemiological studies designed to evaluate biological hypotheses provide evidence of risk for certain pesticides, organic solvents, and products of combustion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2304. doi:10.1158/1538-7445.AM2017-2304