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

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.

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.

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).

This study found that pregnancy and oral contraceptive use had a stronger protective effect on ovarian cancer than other anovulatory factors.