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Vol. 12 Issue 4, Fall 2007

BCERF's Turf Pesticide and Cancer Risk Database
The Ribbon 

By Suzanne Snedeker, Ph.D., BCERF Associate Director of Translational Research

Cohn, Barbara A., Wolff, Mary S., Cirillo, Piera M., and Scholtz, Robert I. (2007). DDT and Breast Cancer in Young Women: New Data on the Significance of Age at Exposure. Environmental Health Perspectives 115, 1406-1414.

Cohn and colleagues examined breast cancer risk and DDT exposure of women diagnosed before the age of 50 who lived in the Oakland, California area. Blood samples were obtained from the women while they were still in their 20s (shortly after they had given birth) and were stored for up to 40 years. The study is unique because it examined risk according to age of exposure, including exposure in a subset of women who were 14 years of age or younger when DDT was introduced for general use in 1945. For instance, while all the women were exposed for the same number of years (1945 to 1963) their age at first possible exposure (their age in 1945) differed considerably.

The investigators analyzed blood samples for three different forms of DDT in both cancer cases and age-matched controls without breast cancer. These forms included p,p’-DDT, the predominant form in technical DDT (“technical DDT” is the form used in insecticide sprays); o,p’-DDT, an estrogenic form that constituted a small proportion of technical DDT; and the persistent metabolite, p,p’-DDE.

While breast cancer risk didn’t differ when the researchers compared levels of o,p’-DDT or p,p’-DDE in cases and controls, differences in breast cancer risk were observed when looked at levels of p,p’-DDT. When they analyzed the results by the age of first exposure in 1945, the authors reported an odds ratio (OR) of 5.4 in the women who were less than 14 years of age in 1945. This means the breast cancer risk was 440% higher in women with the highest levels of p,p’-DDT (highest tercile, the upper third of p,p’-DDT levels) compared to women with the lowest levels of this chemical (lowest tercile). This effect was statistically significant (OR 5.4, 95% CI 1.7-17.1, p for trend 0.01). While the reason for this effect is not known, it is possible that an “imprinting” effect may have occurred. Development of the breast from gestation through puberty has been shown to be affected by exposure to ionizing radiation in humans (Japanese women, atomic bomb survivors) as well as to a variety of endocrine disrupting chemicals in animal studies. These other studies suggest the breast is very sensitive to environmental stressors during this critical window of development.

While this study was small, and results need to be examined carefully (small studies sometimes are more prone to results being due to chance rather than to the chemical being evaluated), it shows the need for studies that evaluate if and how exposures to environmental chemicals during this critical window of breast development affects the lifelong risk of breast cancer. This study focused on breast cancer that occurred by age 50. To what extent early exposures may affect post-menopausal breast cancer risk needs further investigation.

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Last Update 12.11.07