Study reveals link between DDT exposure and breast cancer in women

A five-decade study of US women has revealed that those exposed to high levels of the pesticide DDT ran a four-times higher risk of getting breast cancer.

The study comes as the first of its kind to directly link breast cancer in humans to DDT, which had been in many countries decades ago but continued to be used widely in Africa and Asia.

According to Barbara Cohn of the Public Health Institute in Berkeley, California, and co-author of the study published on Tuesday, environmental chemicals had long been suspected among causes of breast cancer, but until now, there had been few human studies to support this idea.

She added that the 54-year study was the first to provide direct evidence that chemical exposures for pregnant women might have life-long consequences for their daughters' breast cancer risk.

Researchers examined a group of women who were exposed in utero to DDT in the 1960s, when the pesticide was widely used in the US.

The data came from a California programme called Child Health and Development Studies (CHDS), which focused on 20,754 pregnancies among women who were members of the Kaiser Foundation Health Plan from 1959 through 1967.

Of these women, researchers focused on 118 mothers who had daughters who were diagnosed with breast cancer by age 52.

The scientists used stored blood samples from the 118 to get a picture of how much DDT exposure they had when pregnant or shortly after giving birth.

"Independent of the mother's history of breast cancer, elevated levels of DDT in the mother's blood were associated with a nearly four-fold increase in the daughter's risk of breast cancer," said the study.

"Among the women who were diagnosed with breast cancer, 83 per cent had estrogen-receptor positive breast cancer, a form of cancer that may receive signals from the hormone estrogen to promote tumor growth."

According to Elizabeth Ward, senior vice president of intramural research for the American Cancer Society, the group of mothers and daughters the researchers were studying was a "unique resource" for studying potential associations between maternal blood levels of chemicals and risk to their children, The Washington Times reported.

She added what made the study interesting was its analysis of in-utero exposure. However, she added that the number of breast cancer cases was small -- 103 -- so "the results should be interpreted cautiously."