Diethylstilbestrol (DES)
CATEGORY: IARC known, NTP known
USED IN: Prescribed to pregnant women between 1938 and 1971 to prevent miscarriage
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 compared to those who were not exposed to DES in the womb (Bibbo, 1977; Herbst, 1971). Research indicates that 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).
Recent studies examining the mechanisms by which DES might be exerting its carcinogenic effects indicate that the compound activates the same subcellular pathways that estradiol does, both by altering cellular metabolism and interaction with DNA (Saeed, 2009) and by increasing the rate of breast-cell proliferation (Larson, 2006).
