Challenging the convictions of many advocates for patients, a large study, to be published today in The New England Journal of Medicine, has found no evidence that exposure to the chemicals DDT and PCBs increases the risk of breast cancer.
The chemicals, which accumulate in body fat, can act like weak estrogens in the body. And the more estrogen a woman is exposed to, the greater her risk of breast cancer. Previous, smaller studies led to contradictory results, and some had design flaws that made them less than definitive.
The new study, by Dr. David Hunter, an epidemiologist at the Harvard School of Public Health, and his colleagues, was larger and better designed than any before it. It involved nurses who agreed in 1976 to participate in the long-term study, in which their health would be monitored.