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DES, a drug given to women 40 years ago to help prevent miscarriages, may increase the risk of breast cancer in those women’s daughters. According to preliminary results of a long-term study, exposure to DES while in the womb increased risk of breast cancer in women over 40 years of age. Though further data are needed to confirm the results, the study suggests that daughters of women who were given DES may need to be diligent about receiving regular breast cancer screenings. Diethylstilbestrol (DES) is a synthetic estrogen that was commonly used to prevent miscarriages in the 1950s and 1960s. However, subsequent research found that DES was associated with a significantly increased risk of a certain type of vaginal/cervical cancer in the daughters of women who were given the drug. Though no definitive studies have appeared, some researchers believe in utero DES exposure (i.e., exposure to DES while in the womb) also increases the risk of breast cancer. To determine whether exposure to DES in the womb increases the risk of breast cancer later in life, Julie R. Palmer of the Slone Epidemiology Unit at Boston University School of Medicine and colleagues studied 4,821 women who had been exposed to DES and compared them to 2,095 unexposed women. The women were followed for an average of 19 years. The rates of breast cancer among the exposed women’s daughters were then compared with cases of daughters of non-exposed women. While pre-natal DES exposure was not associated with a higher risk of breast cancer in women under 40 years of age, women over 40 who were exposed to DES in the womb were 2.5 times more likely to develop the disease. Thus, while the results are not statistically significant, the researchers said that an overall 40% increased risk of breast cancer from DES exposure warrants further investigation. Approximately 4 million American women were prescribed DES between 1940 and 1971. According to the DES Cancer Network, as many as 10 million Americans, one in 20, has been exposed to DES. DES is associated with a rare form of cancer, clear cell adenocarcinoma of the vagina and cervix. Mothers who were given DES may have a slightly higher risk of breast cancer compared to non-exposed women. No special screening guidelines have been recommended for DES-exposed women. The following guidelines are suggested by several cancer organizations, including the U.S. National Cancer Institute:
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