Dear EarthTalk: Is there a connection between environmental toxins and breast cancer?
—Ben Ward, Virginia Beach, VA
More than 200,000 women are diagnosed with breast cancer each year in the United States, and 20 percent are likely to die from it. Breast cancers among women have climbed steadily in the U.S. and other industrialized nations since the 1940s. More than half of women diagnosed with breast cancer do not have any of the known or traditional risk factors such as family history, hormonal factors or a fatty diet, and researchers suspect that widespread exposure to environmental toxins is triggering the surge.
Strong evidence linking chemicals to breast cancer include studies showing that lifetime chemical exposure to naturally produced estrogens (female hormones produced by the ovaries and other adrenal glands) increases the risk of breast cancer. New evidence also suggests that exposure to compounds that mimic these natural estrogens, such as hormone replacement therapy and oral contraceptives, also increases risk.
Other compounds found to increase breast cancer risk include: polyvinyl chloride, a plastic commonly used in vinyl siding, shower curtains and other products; the gasoline component benzene; and some pesticides and herbicides. Also strongly linked are organic solvents used in manufacturing processes, hydrocarbons produced by the combustion of gasoline and heating oil, and synthetic chemicals like dioxin, a byproduct of the paper bleaching process. Many compounds long ago phased out of use in the U.S.—including DES, a drug taken by pregnant women to prevent miscarriage, the notorious pesticide DDT, and PCBs used in manufacturing—still persist in the environment and can also trigger the disease.
When New York health researchers noticed that breast cancer cases were increasing at alarming rates on Long Island during the 1980s and 1990s, they commissioned the Long Island Breast Cancer Study Project to find out if exposure to some prevalent toxins—including DDT and PCBs—was to blame. Surprisingly, researchers found little evidence to support a definitive connection. However, the study did suggest that these chemicals were linked to enlarged tumor size, meaning that although they may not cause breast cancer, they may contribute to how fast the cancer grows.
Without many direct links between breast cancer and specific contaminants, regulation is unlikely, so women should take precautions on an individual basis. Exercising more, increasing consumption of fruits and vegetables, lowering alcohol intake and quitting smoking are good first steps. Avoiding exposure to contaminants at home or on the job will also help. Meanwhile, environmental groups like the Breast Cancer Fund and Breast Cancer Action are advocating for more Food and Drug Administration (FDA) regulation of chemicals and pressing chemical makers to voluntarily limit the production of certain suspect substances.
CONTACTS: National Long Island Breast Cancer Study Project, http://epi.grants.cancer.gov/LIBCSP/; Breast Cancer Fund, (415) 346-8223, http://www.breastcancerfund.org; Breast Cancer Action, (415) 243-9301, http://www.bcaction.org; U.S. Food and Drug Administration, http://www.fda.gov.