Postmenopausal hormone use and incident ovarian cancer: Associations differ by regimen.

Ovarian cancer has been associated in epidemiologic studies with postmenopausal hormone use. Whether associations differ by hormone regimen, current status or duration of use is unclear. We examined epithelial ovarian cancer incidence in relation to unopposed estrogen (E-only) and estrogen plus progestin (E + P) among 54,436 postmenopausal women of the Cancer Prevention Study II Nutrition Cohort, a US cohort prospectively followed for cancer incidence since 1992. Demographic, medical, reproductive and lifestyle information was collected at enrollment and updated throughout follow-up via self-administered questionnaire. Extended Cox models were used to estimate age- and multivariate-adjusted relative risk (RR) of ovarian cancer according to hormone regimen, current status and duration of use. During 15 years of follow-up, 297 incident cases were identified. Relative to "never" use of hormones, current E-only use was associated with a twofold higher risk [RR 2.07, 95% confidence interval (CI) 1.50-2.85]; each 5-year increment of use was associated with a 25% higher risk (RR 1.25, 95% CI 1.15-1.36); ≥ 20 years of use was associated with a near threefold higher risk (RR 2.89; 95% CI 1.71-4.87; trend p = 0.01). Past E-only use was not significantly associated with ovarian cancer, although a modest increase in risk per each 5-year increment of use was suggested (RR 1.14, 95% CI 0.92-1.41). Neither current nor former E + P use was associated with ovarian cancer risk (RR 1.08, 95% CI 0.86-1.35; RR 1.08, 95% CI 0.68-1.71, respectively, per 5-year increment). These findings suggest that progestins may mitigate some of the detrimental effects of estrogen on the ovarian epithelium.