The association of reproductive factors with risk of non-epithelial ovarian cancer and comparison with serous ovarian cancer

Objective: To examine the association between reproductive factors and risk of non-epithelial ovarian cancer and to compare the associations with those in serous ovarian cancer. Methods: From the Danish Cancer Registry, we identified all ovarian cancer cases (≥20 years old at diagnosis) of germ cell (n = 188), sex cord-stromal (n = 116), or serous (n = 4854) histology during 1982–2016. For each case, 15 age-matched female controls were selected with risk set sampling. Reproductive history was obtained from nationwide registries. Conditional logistic regression was used to estimate odds ratios (ORs) with 95% confidence intervals (CIs) for the association between reproductive factors and the three ovarian cancer types. Results: Compared with nulliparity, ever giving birth was associated with increased odds for germ cell tumors (OR = 1.28, 95% CI: 0.85–1.93) and decreased odds for sex cord-stromal (OR = 0.74, 95% CI: 0.44–1.26) and serous tumors (OR = 0.70, 95% CI: 0.64–0.76). Infertility decreased odds for germ cell tumors (OR = 0.63, 95% CI: 0.23–1.76) but increased odds for sex cord-stromal tumors (OR = 2.20, 95% CI: 0.89–5.43) and serous tumors (OR = 1.97, 95% CI: 1.69–2.30). Finally, use of oral contraceptives decreased the odds for all three tumor types (germ cell: OR = 0.50, 95% CI: 0.29–0.87; sex cord-stromal: OR = 0.40, 95% CI: 0.13–1.22; serous: OR = 0.50, 95% CI: 0.40–0.62). Conclusions: Reproductive factors affected the risk of sex cord-stromal and serous ovarian cancer similarly with decreased risk associated with parity and use of oral contraceptives. Oral contraceptives also seemed to decrease the risk of germ cell tumors, whereas parity was associated with increased risk.