THE NATION - Study finds DDT, breast cancer link - Exposure in childhood is key, quintupling the risk among women with high levels of the pesticide, scientists say.

Women heavily exposed to the pesticide DDT during childhood are five times as likely to develop breast cancer, a new scientific study suggests.

For decades, scientists have tried to determine whether there is a connection between breast cancer and DDT, the most widely used insecticide in history. The UC Berkeley research, based on a small number of Bay Area women, tested a theory that the person's age during exposure was critical, and provided the first evidence of a substantial effect on breast cancer.

"There was very broad exposure to this pesticide, and with this study, we have evidence that women exposed when young were the most affected," said Barbara A. Cohn, director of UC Berkeley's Child Health and Development Studies, who led the study of 129 women. "If this finding holds up, those who were young and more highly exposed could be the women at greatest risk."

"This does speak to a generation of us, the baby boomer generation," said Peggy Reynolds, an epidemiologist at the Northern California Cancer Center and consulting professor at Stanford University School of Medicine. She was not involved in the study.

"There's nothing we can do now about the exposures we may have had back then," Reynolds said. "But it's prudent to say that we should be mindful of the fact that we may have higher risks by virtue of those environmental exposures back then."

Because the pesticide was ubiquitous, the authors wrote, "the public health significance of DDT exposure in early life may be large."

If the early-exposure theory is true, breast cancer rates could rise as the DDT generation ages. Two-thirds of women with invasive breast cancer are 55 or older when they are diagnosed, according to the American Cancer Society.

"A single study doesn't necessarily translate into truth, if you will," Reynolds said. "But a study like this -- which has such dramatic and provocative findings, and is consistent with what we have suspected about early life exposures -- does call for careful examination of the results."