Cancer risk in men exposed in utero to diethylstilbestrol

Background: An association between prenatal diethylstilbestrol (DES) exposu re and cancer in men, especially testicular cancer, has been suspected, but findings from case-control studies have been inconsistent. This study was conducted to investigate the association between prenatal DES exposure and cancer risk in men via prospective follow-up. Methods: A total of 3613 men whose prenatal DES exposure status was known were followed from 1978 throug h 1994, The overall and site-specific cancer incidence rates among the DES- exposed men were compared with those of the unexposed men in the study and with population-based rates. The relative rate (RR) was used to assess the strength of the association between prenatal DES exposure and cancer develo pment. All statistical tests were two-sided. Results: Overall cancer rates among DES-exposed men were similar to those among unexposed men (RR = 1.07; 95% confidence interval [CI] = 0.58 to 1.96) and to national rates (RR = 0 .99; 95% CI = 0.65 to 1.44). Testicular cancer may be elevated among DES-ex posed men, since the RRs for testicular cancer were 3.05 (95% CI = 0.65 to 22.0) times those of unexposed men in the study and 2.04 (95% CI = 0.82 to 4.20) times those of males in the population-based rates. The higher rate o f testicular cancer in the DES-exposed men is, however, also compatible wit h a chance observation. Conclusions: To date, men exposed to DES in utero d o not appear to have an increased risk of most cancers. It remains uncertai n, however, whether prenatal DES exposure is associated with testicular can cer.