Breast Cancer Risk: DDT Linked to Disease
Study Says DDT May Increase Breast Cancer Risk; Experts Disagree
April 24, 2003 -- Exposure to DDT and other pesticides that are believed to alter levels of the female hormone estrogen may increase breast cancer risk. In a study from Belgium, women with breast cancers were more than five times as likely to have DDT residues in their blood.
Though the findings do not prove that so-called estrogenic pesticides promote breast cancer, the study's investigators say they add to the "growing evidence" that suggests a link. But experts contacted by WebMD strongly disagree.
"This study is at odds with about 30 others that do not show an association between these pesticides and breast cancer," says Michael Thun, MD, of the American Cancer Society (ACS). "There is no growing evidence. And the five- or sixfold increase in risk seen in this study would be impossible to miss in the other studies."
DDT was widely used as a pesticide in the United States for almost 30 years before it was banned in 1972. It is one of a handful of manmade chemicals that are widely believed to disrupt hormone levels in humans and animals. Known as organochlorine pesticides or hormonal disrupters, exposure to these chemicals has been implicated in birth defects, immune disorders, and certain cancers.
In the new study, researchers from Belgium's Sart Tilman University Hospital studied blood samples from 159 breast cancer patients who had not begun treatment and 250 women without cancer, matched for age, race, menopausal status, and reproductive and smoking history.
Breast cancer patients were found to be more than five times as likely to have detectable levels of DDT in their blood and more than nine times as likely to have detectable levels of another estrogen-modulating pesticide, hexachlorobenzene (HCB).
Gilbert Ross, MD, who is medical director for the consumer group American Council on Science and Health, says the study had several design problems that may have influenced the findings. He faults the researchers for not including information on the use of hormone replacement therapy and says the matching of the breast cancer cases and controls was not adequate.
"This study is both methodologically flawed and flawed in its basic hypothesis," he says. "There are really no valid studies showing a link between chemical exposures and breast cancer incidence."
Because DDT, and its more easily measured byproduct DDE, are stored in fat, residues can remain in the body for decades. The authors conclude that a dramatic rise in breast cancer incidence may be at least partly explained by past exposures to DDT or other organochlorine pesticides.
Suzanne M. Snedeker, PhD, who heads Cornell University's Program on Breast Cancer and Environmental Risk Factors, says the vast majority of studies have shown no link between pesticide exposure and breast cancer incidence in white women, but the evidence is far less conclusive in women of other races.
"Most people don't realize that the peak use of DDT in this country was in the early 1960s in cotton fields," she tells WebMD. "The people who worked those crops were largely African American, and we don't have very good data on breast cancer in these women."