News Clipping: DES and Breast Cancer Risk

by Katrina Kahl

Daughters of women who took diethylstilbestrol (DES) during pregnancy may have double the risk of breast cancer compared to women not exposed to the drug, according to a study published in the August 2006 issue of Cancer, Epidemiology, Biomarkers, and Prevention.1 DES, a synthetic estrogen, was used by as many as 2 million women in the United States during the 1940s to 1960s to reduce the risk of miscarriage (a study in 1953 indicated the drug had no benefit in reducing this risk). The drug was discontinued when it was found to greatly increase the risk of rare vaginal and cervical cancers in the daughters of women who took DES. (Sons of these women also had health effects). Subsequently, it was discovered that DES is also responsible for an increased risk of breast cancer in women who took the drug.

In this latest study, researchers focused on prenatal exposure to DES by comparing a group of women whose mothers used DES during pregnancy to women who were not exposed. Taking into account known risk factors for breast cancer, the final results showed 76 cases of breast cancer in the group of women exposed to DES (4,817 women in total) versus 26 cases in the unexposed group (2,073 women in total). Although no increase in risk was found for women younger than 40 years of age, for women over 40, prenatal exposure to DES was found to almost double the risk of breast cancer. The risk may be even greater for women over 50, although the small number of women in this category made it difficult to determine if the increase was statistically significant. Additionally, researchers found a dose-related effect—the daughters of women who took higher doses of DES had a greater risk.

This study lends evidence to the hypothesis that breast cancer risk can be influenced by hormonal exposures that occur in the womb. Women should ask their mothers about DES use during or just before pregnancy. Women exposed to DES should get regular clinical breast exams and mammograms (at the appropriate ages), and seek information about the risks, benefits, and limitations of the different breast cancer detection methods.2

1 Julie R. Palmer, et al., “Prenatal Diethylstilbestrol Exposure and Risk of Breast Cancer,” Cancer, Epidemiology, Biomarkers, and Prevention 15(8), August 2006, pp. 1509-1514.

2 For more information, see BCA’s policy on mammography screening and new technologies.

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