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06 November 2016

Institutes in the Lead: Identifying Environmental Factors in Breast Cancer

The Interagency Breast Cancer and Environmental Research Coordinating Committee pointed out that only about 10–11% of federally funded breast cancer research focuses on environmental contributions to breast cancer. “Breast cancer prevention is underfunded at the federal level in both research and public health programs, and future investments must focus on this area,” they wrote.  “Enhanced investments would facilitate sustained coordination across research and regulatory agencies with the objective of reducing or eliminating harmful environmental exposures and modifying social and lifestyle factors implicated in breast cancer.”

Institutes in the Lead: Identifying Environmental Factors in Breast Cancer
Environ Health Perspect; DOI:10.1289/ehp.124-A199

Background image: © demonique/Shutterstock

Nate Seltenrich covers science and the environment from Petaluma, CA. His work has appeared in High Country News, Sierra, Yale Environment 360, Earth Island Journal, and other regional and national publications.

In a way, it all started in Long Island, New York. The year was 1993. An apparent cluster of breast cancer cases had been discovered in Nassau and Suffolk counties, and some residents worried that pesticide applications on former farmland could be to blame.1 They demanded an investigation. The U.S. Congress soon agreed and asked the National Institute of Environmental Health Sciences (NIEHS) and the National Cancer Institute (NCI) to research the potential role of environmental exposures in these cases.1 In the decades since, these institutes have conducted and funded countless studies on potential environmental risk factors for breast cancer.2

Breast cancer, like many cancers, is a challenging disease to understand thoroughly because its causes include both genetic and environmental factors. Breast cancer also takes many years to develop, making it difficult for researchers to identify environmental factors “after the fact” that might have contributed to the initiation of the cancer.

Breast tissue receives hormonal signals from several endocrine organs (including the placenta, ovaries, pancreas, and thyroid) and responds to a wide range of hormones (including estrogen, progesterone, insulin, and thyroxine).3 Breast cancer researchers today are interested in exposures not only to chemicals that pose a cancer risk by altering DNA (in other words, classical carcinogens) but also to substances that may act on the body in other ways, such as endocrine disruptors.

“Endocrine disruptors are not expected to act as carcinogens per se—they don’t necessarily cause mutations or formation of DNA adducts,” explains Suzanne Fenton, leader of the NIEHS intramural Reproductive Endocrinology Group. “Rather, they cause a shift in how the body responds to normal hormones that the body produces all the time.”

Over time, studies examining how chemicals might contribute to breast cancer initiation have become better focused and more hypothesis-driven, says Deborah Winn, deputy director of the NCI’s Division of Cancer Control and Population Sciences. “The technology’s better, our questions are sharper, and the evidence is mounting,” she says. “I think we’re getting closer to [understanding environmental factors in a way] that’s clearer and that we can say something definitive about.”4,5

Long Island Breast Cancer Study Project

At the time of the hypothesized Long Island cluster, breast cancer incidence nationwide averaged about 130 diagnoses per 100,000 people per year.6 In New York state from 1988 to 1992, rates were below average, about 122 cases per 100,000. But incidence in Nassau and Suffolk counties during this period was considerably higher: 139 and 133 cases per 100,000, respectively.1

The NIEHS and the NCI established a research study called the Long Island Breast Cancer Study Project (LIBCSP) to find out why. This effort included five distinct case–control sub-studies designed to address specific environmental exposures while controlling for other risk factors, such as age and reproductive history. Their goal was to evaluate whether increased risk of breast cancer was associated with high-priority exposures including organochlorine pesticides (such as DDT and its metabolite DDE); polychlorinated biphenyls (PCBs, once widely deployed in electrical equipment); polyaromatic hydrocarbons (PAHs, by-products of incomplete combustion); and electromagnetic fields (such as those generated by power lines and electric blankets).

Investigators ultimately reported two significant associations, both of which came from the project’s largest sub-study, the Breast Cancer and the Environment on Long Island Study. One showed that the odds of breast cancer were 50% higher in women with the highest levels of PAH-DNA adducts (which are biomarkers of exposure),7 and the other that the odds of breast cancer were almost 3 times higher in women living within 1 mile of hazardous waste sites containing organochlorine pesticides versus those who lived farther away.8...

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