Lifetime ovulatory years and risk of epithelial ovarian cancer: a multinational pooled analysis

Abstract Background The role of ovulation in epithelial ovarian cancer (EOC) is supported by the consistent protective effects of parity and oral contraceptive (OC) use. Whether these factors protect through anovulation alone remains unclear. We explored the association between lifetime ovulatory years (LOY) and EOC. Methods LOY was calculated using 12 algorithms. Odds ratios (ORs) and 95% confidence intervals (CIs) estimated the association between LOY or LOY components and EOC among 26,204 controls and 21,267 cases from 25 studies. To assess whether LOY components act through ovulation suppression alone, we compared beta coefficients obtained from regression models to expected estimates assuming one year of ovulation suppression has the same effect regardless of source. Results LOY was associated with increased EOC risk (ORs per year increase: 1.014 (95%CI 1.009-1.020) to 1.044 (95%CI 1.041-1.048)). Individual LOY components, except age at menarche, also associated with EOC. The estimated model coefficient for OC use and pregnancies were 4.45 times and 12-15 fold greater than expected, respectively. LOY was associated with high-grade serous (HGSOC), low-grade serous (LGSOC), endometrioid, and clear cell histotypes (ORs per year increase: 1.054, 1.040, 1.065, and 1.098, respectively), but not mucinous tumors. Estimated coefficients of LOY components were close to expected estimates for HGSOC but larger than expected for LGSOC, endometrioid, and clear cell histotypes. Conclusions LOY is positively associated with non-mucinous EOC. Differences between estimated and expected model coefficients for LOY components suggest factors beyond ovulation underlie the associations between LOY components and EOC in general and for non-HGSOC.