Do Chemicals Influence Breast Density?

Silent Spring Institute

A new study by Silent Spring Institute on adolescent girls aims to shed light on the influence of environmental chemicals on breast density, a known risk factor for breast cancer. At issue is whether exposure to harmful chemicals in consumer products during this important period of development leads to increased breast density, and as a result, an increased susceptibility to breast cancer later in life.

As states across the country enact laws requiring doctors to inform women of their breast density based on their mammograms, the subject has generated widespread interest and debate among physicians, patients, and advocates alike. In general, women with dense breasts have a higher risk of developing breast cancer. Dense tissue also makes it harder for radiologists to see tumors on x-rays. Why some women develop dense breasts and others don’t is not well understood.

Chemicals in the environment might play a role. Experiments in animals show that exposure to hormone-disrupting chemicals—common chemicals which can be found in everyday consumer products—can alter breast tissue in ways that make the tissue more sensitive to hormones. And studies in people have shown that early exposure to hormone-disrupting chemicals can increase the risk for later development of breast cancer.

To learn whether exposure to these chemicals during puberty affects breast density, researchers at Silent Spring Institute and their collaborators are focusing on a group of 400 Latino girls in Santiago, Chile. The group is unique in that researchers have been following these girls since age four, collecting data on developmental milestones such as breast development and age of first menstruation.

Using urine and blood samples, the researchers will measure the girls’ exposure to three different hormone disruptors: PFOA, BBP, and Zeranol. Perfluorooctanoic acid (PFOA) is commonly used in food packaging and in non-stick coatings on cookware, and BBP (butylbenzyl phthalate) is found in flexible plastics and vinyl flooring. Zeranol is a synthetic hormone widely used in the U.S. and Chilean beef industry, although its use is prohibited in Europe. The researchers will look at whether exposure to these chemicals leads to specific changes in the composition of the girls’ breast tissue.

“These early life exposures are critical,” says Julia Brody, executive director of Silent Spring Institute. “The body is changing rapidly and is vulnerable to chemical exposures. So, it’s vital that we study this important window of susceptibility.” The project is one of seven efforts nationwide being funded through the Breast Cancer and the Environment Research Program (BCERP)—a National Institutes of Health (NIH) program focused on breast cancer prevention and environmental health.

Karin Michels, associate professor in the department of obstetrics, gynecology, and reproductive biology at Brigham and Women’s Hospital in Boston, is leading the effort along with Silent Spring Institute. Other members include Jose Russo, director of the Breast Cancer and the Environment Research Center at Fox Chase Cancer Center in Philadelphia and Camila Corvalan, assistant professor at the Institute of Nutrition and Food Technology at the University of Chile in Santiago.

A major component of the project will be to disseminate and translate results from the study to the parents of the girls enrolled, and to engage the local community in breast cancer prevention. Using Silent Spring’s extensive experience in community-engaged research, the researchers will provide the parents with individualized reports on their daughters’ results, as well as educational materials on breast cancer and environmental health. The study’s findings will be translated to inform consumers, environmental health organizations, and breast cancer advocates in the United States as well.

“In order to truly understand the causes of breast cancer, we need to better understand the possible relationship between environmental chemicals and breast density,” says Brody. “And that relationship may begin early in life.”

Contributed by Silent Spring Institute