CATEGORY*: IARC known, NTP known
USED IN: Prescribed to pregnant women between 1938 and 1971 to prevent miscarriage
THE GIST: Between 1938 and 1971 doctors prescribed DES for millions of pregnant women to prevent miscarriages, culminating in a medical tragedy that has affected at least 5 million people. Daughters of women who took the drug were found to have higher rates of an extremely rare vaginal cancer, in addition to breast cancer. The drug was banned in 1971.
State of the Evidence on Diethylstilbestrol (DES)
The clearest evidence that a synthetic estrogen can increase risk for cancer decades later comes from the tragic experience with diethylstilbestrol (DES).
Between 1938 and 1971, doctors prescribed DES for millions of pregnant women to prevent miscarriages. The drug was banned when daughters of women who took the drug were found to have higher rates of an extremely rare vaginal cancer than women who were not exposed to DES in the womb (Bibbo 1977; Herbst, 1970). DES exposure is also associated with an increased risk of breast cancer in the women who took it during the 1950s (Colton, 1993; Titus-Ernstoff, 2001).
In a follow-up study of daughters who were exposed prenatally to DES, a nearly twofold increase in breast cancer risk was observed in women older than age 40. An even greater effect was found for women over the age of 50, although relatively few of the daughters had yet reached that age at the time of the study (Palmer, 2006; Troisi, 2007). Women exposed in utero who had the most severe abnormalities of their vaginal epithelial cells (an indicator of exposures to higher doses of DES) also had a higher risk for developing breast cancer (Hoover, 2011).
Studies examining the mechanisms by which DES might be exerting its carcinogenic effects indicate that the compound activates the same subcellular pathways as estradiol. They both act through altering cellular metabolism and through interactions with DNA (Saeed, 2009), and increase the rate of breast-cell proliferation (Larson, 2006).
*For chemicals that have been shown to be carcinogens, we provide classifications from two authoritative bodies: the International Agency for Research on Cancer (IARC, an international body) and the National Toxicology Program (NTP, a division of the U.S. Department of Health and Human Services). We have categorized endocrine-disrupting compounds where the body of peer-reviewed research indicates a strong foundation for doing so.