Menstrual and reproductive factors and exogenous hormone use and risk of transitional cell bladder cancer in postmenopausal women

The incidence of cancer of the urinary bladder is three- to five-fold lower in women than in men. This difference may be partially explained by lower exposure to cigarette smoking and occupational chemicals. In addition, female endogenous hormones may also play a protective role in the etiology of this disease. However, limited information is available from cohort studies that have examined reproductive factors and hormone use in relation to the risk of bladder cancer. We assessed the association of menstrual and reproductive factors and exogenous hormone use with the risk of incident transitional cell cancer of the urinary bladder in a cohort of 145 548 postmenopausal women (ages 50-79 years at baseline) enrolled in the Women's Health Initiative. Over 12.7 years of follow-up, 480 cases of transitional cell bladder cancer were identified. Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the exposures of interest. Relative to nulliparous women, parous women had a reduced risk of transitional cell cancer: multivariable-adjusted HR 0.77, 95% CI 0.59-1.01; however, there was no clear trend with increasing number of births. Risk was significantly increased in women with a history of at least two miscarriages (HR 1.52, 95% CI 1.15-2.00). Neither other reproductive variables we studied nor the use of exogenous hormones, including type of hormone therapy, were associated with altered risk of bladder cancer. In conclusion, in this large prospective study of postmenopausal women, we found limited evidence for associations of reproductive factors or exogenous hormone use with the risk of bladder cancer.