CANCER RISK IN WOMEN EXPOSED TO DIETHYLSTILBESTROL IN-UTERO

Context. - The association between in utero exposure to diethylstilbes trol (DES) and clear cell adenocarcinoma (CCA) of the vagina and cervi x is well known, yet there has been no systematic study of DES-exposed daughters to determine whether they have an increased risk of other c ancers, As many as 3 million women in the United States may have been exposed to DES in utero. Objective. - To determine whether women expos ed to DES in utero have a higher risk of cancer after an average of 16 years of follow-up. Design. - A cohort study with mailed questionnair es and medical record review of reported cancer outcomes. Participants . - A cohort of 4536 DES-exposed daughters (of whom 81% responded) and 1544 unexposed daughters (of whom 79% responded) who were first ident ified in the mid-1970s. Main Outcome Measures. - Cancer incidence in D ES-exposed daughters compared with population-based rates and compared with cancer incidence in unexposed daughters. Results. - To date, DES -exposed daughters have not experienced an increased risk for all canc ers (rate ratio, 0.96; 95% confidence interval [CI], 0.58-1.56) or for individual cancer sites, except for CCA. Three cases of vaginal CCA o ccurred among the exposed daughters, resulting in a standardized incid ence ratio of 40.7 (95% CI, 13.1-126.2) in comparison with population- based incidence rates. The rate ratio for breast cancer was 1.18 (95% CI, 0.56-2.49); adjustment for known risk factors did not alter this r esult. Conclusions. - Thus far, DES-exposed daughters show no increase d cancer risk, except for CCA. Nevertheless, because exposed daughters included in our study were, on average, only 38 years old at last fol low-up, continued surveillance is warranted to determine whether any i ncreases in cancer risk occur during the menopausal years.