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Dick Clapp, CHE Partner
Between 1940 and 1971, a synthetic form of estrogen called diethylstilbestrol (DES) was prescribed to pregnant women to prevent miscarriage and premature labor. This practice changed abruptly, though, after the New England Journal of Medicine published a dramatic new finding from a study of young women diagnosed with a rare cancer in two Boston hospitals. The authors of the study, using a hospital-based matched case-control design, reported a startling excess of clear cell adenocarcinoma of the vagina in women whose mothers had taken DES to prevent pregnancy loss. Seven of the eight cases were born to mothers who were prescribed and took DES during their pregnancy, while none of the mothers of the controls had taken the drug.
The probability of this outcome was estimated as less than 0.00001; although not reported in the published article, the odds ratio would have been infinity. Given the rarity of this cancer, and the strength of the association reported in this careful study, this result was so convincing that an accompanying editorial in the same issue of the journal said “it seems prudent for physicians to use caution in prescribing estrogenic substances during pregnancy.” This cautionary language was putting physicians on notice that prenatal exposure to DES appears to cause cancer in offspring. Later the same year, the U.S. Food and Drug Administration issued a Drug Bulletin for physicians saying the prescription of the drug was contra-indicated during pregnancy.
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