Long-term cancer risk in women given diethylstilbestrol (DES) during pregnancy

From 1940 through the 1960s, diethylstilbestrol (DES), a synthetic oestroge n, was given to pregnant women to prevent pregnancy complications and losse s. Subsequent studies showed increased risks of reproductive tract abnormal ities, particularly vaginal adenocarcinoma, in exposed daughters, An increa sed risk of breast cancer in the DES-exposed mothers was also found in some studies. In this report, we present further follow-up and a combined analy sis of two cohorts of women who were exposed to DES during pregnancy. The p urpose of our study was to evaluate maternal DES exposure in relation to ri sk of cancer, particularly tumours with a hormonal aetiology. DES exposure status was determined by a review of medical records of the Mothers Study c ohort or clinical trial records of the Dieckmann Study. Poisson regression analyses were used to estimate relative risks (RR) and 95% confidence inter vals (CI) for the relationship between DES and cancer occurrence. The study results demonstrated a modest association between DES exposure and breast cancer risk, RR = 1.27 (95% CI = 1.07-1.52). The increased risk was not exa cerbated by a family history of breast cancer, or by use of oral contracept ives or hormone replacement therapy. We found no evidence that DES was asso ciated with risk of ovarian, endometrial or other cancer. (C) 2001 Cancer R esearch Campaign http://www.bjcancer.com.