Background: The influence of prenatal diethylstilbestrol (DES) exposure on cancer incidence among middle-aged men has not been well-characterized. We investigated whether exposure to DES before birth impacts overall cancer risk, and risk of site-specific cancers. Methods: Men (mean age in 2016 ¼ 62.0 years) who were or were not prenatally DES exposed were identified between 1953 and 1994 and followed for cancer primarily via questionnaire approximately every 5 years between 1994 and 2016. The overall and site-specific cancer rates of the two groups were compared using Poisson regression and proportional hazards modeling with adjustment for age. Results: DES exposure was not associated with either overall cancer [hazard ratio (HR), 0.94; 95% confidence interval (CI), 0.77–1.15] or total prostate cancer rates (HR, 0.95; 95% CI, 0.68–1.33), but was inversely associated with urinary tract cancer incidence (HR, 0.48; 95% CI, 0.23–1.00). Conclusions: There was no increase in either overall or prostate cancer rates among men prenatally DES exposed relative to those unexposed. An unexpected risk reduction was observed for urinary system cancers among the exposed relative to those unexposed. These findings suggest that prenatal DES exposure is unlikely to be an important contributor to cancer development in middle-aged men. Impact: The results of this study could lend reassurance to middle-aged men who were prenatally DES exposed that their exposure does not adversely influence their overall cancer risk.
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