Lifetime ovulatory cycles and ovarian cancer risk in 2 Italian case-control studies

Objective: Several factors that are related to ovulation are relevant to ovarian cancer risk, but it is unclear whether they can be included in a single definition of years of ovulation. Study design: We considered data from 2 case-control studies of ovarian cancer that were conducted in Italy and included 1822 histologically confirmed cases and 4631 control subjects who were hospitalized for acute conditions. Results: As compared with the lowest quartile, the odds ratios of ovarian cancer were 1.60 (95% CI, 1.31-1.95), 1.65 (95% CI, 1.34-2.03), and 1.81 (95% CI, 1.47-2.23) for increasing quartiles of lifetime ovulatory cycles. For 1 year of ovulation avoided, the continuous odds ratios were 0.975 (95% CI, 0.965-0.985) for total ovulatory cycles, 0.91 (95% CI, 0.87-0.95) for parity-related anovulations, 0.90 (95% CI, 0.76-1.06) for abortions, 0.92 (95% CI, 0.87-0.97) for oral contraceptive use, 0.99 (95% CI, 0.96-1.03) for age at menarche, and 0.97 (95% CI, 0.95-0.98) for age at menopause. Women who reported high numbers of ovulatory cycles and family history of ovarian/breast cancers had an odds ratio of 3.27 (95% CI, 2.44-4.36). Conclusion: This study found that pregnancy and oral contraceptive use had a stronger protective effect on ovarian cancer than other anovulatory factors.