Breast Cancer: It's Not All In The Genes

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Air Pollution

Air pollution contains polyaromatic hydrocarbons (PAHs) among many other chemicals linked to breast cancer in laboratory animals. "When people think breast cancer, they don't immediately think air pollution," says Julia Green Brody, PhD, a scientist at the Silent Spring Institute in Massachusetts. "But there is an increasing body of research that suggests to us that air pollution might play a role in breast cancer risk because it contains chemicals that are known to cause breast cancer in animals."

Pesticides

Another potential source of chemical exposures is pesticides. Among women living on Long Island, NY, breast cancer risk is higher in those with lifetime self-reported use of residential pesticides, a study in the March 2007 American Journal of Epidemiology found. Long-banned DDT still has a place on the list of potential exposures linked to breast cancer. Millions of American women were exposed to DDT from insect control programs in the 1940s and 1950s. The study found that women exposed to DDT in childhood (as measured by the presence of DDT in their blood donated during the 1960s as part of an unrelated study) had a greater risk of breast cancer than women born before DDT was used. Whereas previous studies of DDT exposure and breast cancer found no link, this study was able to test for DDT in the blood of women closer to the time of exposure. "Women who could have been exposed under the age of 14 to DDT are the ones that had the largest risk ... [and] nearly every women in the U.S. during those years would have been exposed," says Barbara Cohn, Ph.D., of the Public Health Institute in Berkeley, California.

The critical aspect of this study is that it addresses when exposures occurred. Evidence is accumulating that exposure during childhood leads to a greater increase in risk of breast cancer. For example, girls exposed to radiation in Japan during World War II went on to have a higher rate of breast cancer than women who were exposed as adults. "The time of exposure seems to be important," says Mary S. Wolff, Ph.D., an environmental scientist at Mount Sinai School of Medicine. "Exposure very early in life or post-natally can cause changes that you don't see if animals are exposed after birth or after pubertal development."

Second-hand smoke

The link between second-hand smoke and breast cancer remains controversial. Scientists at the California Environmental Protection Agency, however, are convinced that environmental tobacco smoke can cause breast cancer, at least for younger, premenopausal women, based on a review of the studies published in a February 2007 issue of Preventative Medicine. For reasons that are still unclear, the risk of breast cancer in women who actively smoke is not all that much greater than women who are exposed to passive smoke.