The Estimated Effect of Oral Contraceptive Use on the Cumulative Risk of Epithelial Ovarian Cancer

OBJECTIVE:To determine the effect of oral contraceptive (OC) use on the cumulative incidence of epithelial ovarian cancer from ages 20-40, 20-50, and 20-55 years among four groups of womenpositive family history, negative family history, parous, and nulliparous. METHODS:Cancer and Steroid Hormone Study data were combined with data from the Surveillance, Epidemiology, and End Results Network to provide estimates of the agespecific incidence rates of epithelial ovarian cancer among never-users of OCs in the four specified groups of women. These rates provided the basis for calculating cumulative incidences. The rates in women using OCs were estimated from meta-analyses of the epidemiologic literature, using regression equations expressing the log-relative rate of epithelial ovarian cancer as a function of duration of use and recency. RESULTS:In all four groups, the cumulative number of epithelial ovarian cancer cases estimated to occur per 100,000 OC users, compared to never-users, decreased with increasing duration of OC use. Our results suggest that 5 years of OC use by nulliparous women can reduce their ovarian cancer risk to the level seen in parous women who never use OCs, and that 10 years of OC use by women with a positive family history can reduce their risk to a level below that for women whose family history is negative and who never use OCs. CONCLUSION:These data represent the first published estimates of the effect of OC use on the cumulative incidence of epithelial ovarian cancer by family history and by parity. The demonstrated substantial noncontraceptive benefit from OCs justifies their judicious use as a potentially powerful resource for primary prevention in women at high risk of ovarian cancer.