Researchers may have uncovered a novel strategy to predict whether synthetic chemicals may cause breast cancer by examining their specific traits, according to a recent study published by Kay et al in Environmental Health Perspectives.
Background
The incidence of breast cancer—the most common cancer type in the United States—may be increasing among young women, a trend that cannot be explained by genetics. With tens of thousands of synthetic chemicals on the market and new ones constantly in development, determining which ones might be harmful has been challenging for the federal agencies that regulate them as well as manufacturers.
“We need new tools to identify environmental exposures that could be contributing to this trend so we can develop prevention strategies and reduce the burden of the disease,” emphasized lead study author Jennifer Kay, PhD, a research scientist at the Silent Spring Institute.
Over the past decade, there has been growing evidence that environmental chemicals are important contributing factors in the development of cancer. Recent studies have established links between breast cancer and pesticides, hair dyes, and air pollution. Other studies have indicated that exposure to hormone-disrupting chemicals early in life—in the womb or during puberty—can alter breast development in ways that could increase the risk of cancer later in life. However, in order to observe these associations, researchers often have to wait until hundreds or thousands of individuals have been exposed to a chemical to determine a correlation many years later.
“It’s not feasible, nor is it ethical, to wait that long,” emphasized co–study author Ruthann Rudel, MS, Director of Research at the Silent Spring Institute. “And it’s another reason why we need better tools for predicting which chemicals are likely to lead to breast cancer so we can avoid those exposures,” she continued.
Study Methods and Results
In the recent study, Dr. Kay and her colleagues used the International Agency for Cancer Research, the National Toxicology Program, the U.S. Environmental Protection Agency (EPA), and the National Cancer Institute databases to find chemicals that have been found to cause mammary tumors in animals.
The researchers then examined data from the EPA’s ToxCast program to determine which endocrine-disrupting chemicals may alter the body’s hormones in ways that could promote breast cancer. They searched specifically for chemicals capable of activating the estrogen receptor as well as those that cause cells to make more estrogen or progesterone, an established risk factor for breast cancer.
After conducting their analyses, the researchers identified a total of 921 chemicals that could promote the development of breast cancer—90% of which individuals may be exposed to in common consumer products, foods and beverages, pesticides, drugs, and workplaces. The researchers noted that 278 of the chemicals caused mammary tumors in animals, and 420 of them both caused DNA damage and altered hormones. They revealed that the chemicals that caused mammary tumors in animals were more likely to have DNA-damaging and hormone-disrupting characteristics compared with the ones that didn’t cause the tumors in animals.
“Historically, chemicals that cause mammary tumors in animals were seen as the best predictors of whether they might cause breast cancer in humans, but animal studies are expensive and time-consuming, which is why so many chemicals have not been tested. Our findings show that screening chemicals for these hormonal traits could be an effective strategy for flagging potential breast carcinogens,” stated Dr. Rudel.
Further, over half of the chemicals caused cells to produce greater levels of estrogen or progesterone, and about one-third of them activated the estrogen receptor.
“Breast cancer is a hormonal disease, so the fact that so many chemicals can alter estrogen and progesterone is concerning,” stressed Dr. Kay.
Conclusions
The researchers hope their new study might have implications for how the EPA assesses chemicals for safety. For instance, the chemicals identified in the study include more than 30 pesticides that have been approved by the EPA for use despite evidence linking the chemicals to mammary tumors.
In the fall of 2023, the EPA proposed a new strategic plan to ensure that pesticides are evaluated for their effects on hormones. The researchers expect their new comprehensive list of breast cancer–relevant chemicals—which includes hundreds of endocrine disruptors—to inform the agency’s plan and better protect the public from harmful exposures.
“This new study provides a roadmap for regulators and manufacturers to quickly flag chemicals that could contribute to breast cancer in order to prevent their use in consumer products and find safer alternatives,” concluded Dr. Kay
Disclosure: The research in this study was funded by the California Breast Cancer Research Program and charitable donations made to the Safer Chemicals Program at the Silent Spring Institute. For full disclosures of the study authors, visit ehp.niehs.nih.gov.
