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Long and irregular menstrual cycles, polycystic ovary syndrome, and ovarian cancer risk in a population‐based case‐control study

Long and irregular menstrual cycles, a hallmark of polycystic ovary syndrome (PCOS), have been associated with higher androgen and lower sex hormone binding globulin levels and this altered hormonal environment may increase the risk of specific histologic subtypes of ovarian cancer. We investigated whether menstrual cycle characteristics and self‐reported PCOS were associated with ovarian cancer risk among 2,041 women with epithelial ovarian cancer and 2,100 controls in the New England Case‐Control Study (1992–2008). Menstrual cycle irregularity, menstrual cycle length, and PCOS were collected through in‐person interview. Unconditional logistic regression models were used to calculate odds ratios (OR) and 95% confidence intervals (95% CIs) for ovarian cancer risk overall, and polytomous logistic regression to evaluate whether risk differed between histologic subtypes. Overall, we observed no elevation in ovarian cancer risk for women who reported periods that were never regular or for those reporting a menstrual cycle length of >35 days with ORs of 0.87 (95% CI = 0.69–1.10) and 0.83 (95% CI = 0.44–1.54), respectively. We observed no overall association between self‐reported PCOS and ovarian cancer (OR = 0.97; 95% CI = 0.61–1.56). However, we observed significant differences in the association with menstrual cycle irregularity and risk of ovarian cancer subtypes (pheterogeneity = 0.03) as well as by BMI and OC use (pinteraction < 0.01). Most notable, menstrual cycle irregularity was associated with a decreased risk of high grade serous tumors but an increased risk of serous borderline tumors among women who had never used OCs and those who were overweight. Future research in a large collaborative consortium may help clarify these associations.