EcoCancers: Do Environmental Factors Underlie a Breast Cancer Epidemic?
Raloff, Janet, Science News
Do environmental factors underlie a breast cancer epidemic?
Throughout countries rich and poor, industrial and rural, breast cancer incidence is on the rise. No one knows what's fueling that increase, especially since recent studies have all but thrown out what had been the primary suspect: dietary fat.
In following up a variety of promising new leads, oncologists and epidemiologists have discovered a common thread that appears to tie together many tantalizing alternative suspects: They all appear able to boost the amount of estrogen in the body Most carcinogens disrupt the body's normal operations by throwing a monkey wrench into its genetic machinery Thus, scientists typically scout for potential carcinogens by investigating a suspect agent's ability to break, disable, mutate, or otherwise alter DNA.
But in a number of laboratories around the world, researchers are now investigating other, more circuitous mechanisms to explain breast cancer's rise. Though far from conclusive, their findings suggest that an unintended side effect of industrialization is an environment that bathes its inhabitants in a sea of estrogenic agents. Some of these agents, such as pesticides and ingredients in plastics, mimic the hormone estrogen in their effects on the body Others, such as magnetic fields and certain combustion by-products, can boost the concentration of estrogens circulating in the bloodstream.
And that's beginning to worry toxicologists and epidemiologists, because factors that increase a woman's lifetime exposure to estrogen, such as early puberty and late menopause, are among the leading known risk factors for breast cancer.
Although scientists don't understand exactly how estrogen fosters breast cancer, they do know that this steroid hormone stimulates cell proliferation in the breasts during each menstrual cycle. To some, this suggests that an excess of estrogen might drive the high rate of cell proliferation characteristic of cancer. But even after accounting for estrogen and other known risk factors, "we still cannot explain 60 to 70 percent of breast cancers:' observes Devra Lee Davis, a toxicologist with the Department of Health and Human Services.
However, she points out, this accounting ignores a population's exposure to what she terms "xenoestrogens." Such agents are not produced in the body, she explains, but when they interact with the body, they "have the effect of functioning directly or indirectly as estrogens and thereby increasing your lifetime exposure to estrogens."
In the forthcoming August ENVIRONMENTAL HEALTH PERSPECTIVES, Davis and researchers at five medical centers will review studies that together provide what they believe to be compelling evidence of widespread human exposure to xenoestrogens. They note, for example. that many nearly ubiquitous pollutants possess estrogenic properties. These include pesticides such as DDT, heptachlor, and atrazine, as well as several polycyclic aromatic hydrocarbons (PAHs), petroleum by-products, and polychlorinated biphenyls (PCBs). Indeed, they note, many of these pollutants are known to induce or promote mammary cancers in lab animals.
Human data, though scant, also suggest that several of these chemicals especially certain chlorinated organic compounds and PAHs - may increase a woman's risk of breast cancer. For instance, Davis and her coauthors cite studies showing elevated breast cancer rates in women who work in the chemical industry, who were exposed to PCBs in Japan, who were exposed to PAH contamination in drinking water, or who carried high concentrations of DDT in breast tissue (SN: 4/24/93, p. 262).
The researchers conclude that xenoestrogens may play a significant role in breast cancer worldwide. And if that's true, says Davis, identifying the most pervasive, persistent, and potent of these could go a long way toward helping shape strategies to thwart the upward trend in breast cancer incidence. …