Cancer risk among women exposed to exogenous estrogens during pregnancy.

A cohort of 3,139 obstetric patients, who delivered children between 1946 and 1965, was followed retrospectively to assess the relationship between exposure to diethylstilbestrol [(DES) CAS: 56-53-1; alpha, alpha'-diethyl-4,4'-stilbenediol] or other estrogenic substances during pregnancy and subsequent cancer incidence. Among the 1,531 women exposed to DES, the relative risk (RR) for all cancers was 1.46 [95% confidence interval (CI), 1.07-2.00]. The RR for cancers of the breast, cervix, and ovary were 1.37 (adjusted), 1.40, and 2.83, respectively, but none of these estimates was statistically significant. For breast cancer an RR in excess of 2.28 can be excluded, with 95% CI for doses averaging 2,100 mg. Within the exposed group there was no evidence for a dose-response relationship.