A prospective cohort study of oral contraceptive use and ovarian cancer among women in the United States born from 1947 to 1964

Oral contraceptives (OCs) have been consistently associated with a reduced ovarian cancer risk; however, most previous studies included women in older birth cohorts using high-dose OC formulations. We assessed OC use, including type and dose, and ovarian cancer risk among women born between 1947 and 1964 using more recent formulations. We included 110,929 Nurses' Health Study II participants. Women reported duration of OC use and brands used from age 13 to baseline (1989) and every 2 years thereafter through 2009. We categorized brands by estrogen and progestin type, dose, and potency, and used Cox proportional hazards models, adjusted for age, calendar time, reproductive factors, and body mass index, to assess associations with ovarian cancer. Over 2,178,679 person-years of follow-up, we confirmed 281 cases. At baseline, 83% of participants reported ever using OCs. Compared to never use, we observed an increased risk of ovarian cancer with ae6 months of OC use (HR 1.82; 95% CI 1.13-2.93) but a non-significant 57% (95% CI 0.18-1.03) decreased risk with ae15 years of OC use. The increased risk among short-term users (ae1 year) was restricted to OCs containing mestranol (HR 1.83; 95% CI 1.16-2.88) and first-generation progestin (HR 1.72; 95% CI 1.11-2.65). The associations between OCs and ovarian cancer observed for this younger birth cohort differ substantially from the results of previous cohort studies, possibly reflecting changes in OC formulations and use patterns over time, although these results could be due to chance. Additional studies should evaluate newer OC formulations and ovarian cancer risk.