Background: Women using unopposed estrogens during menopause are at increased risk of ovarian cancer. It is uncertain whether oestrogen plus progestin therapy exerts similar effects.
Methods: We evaluated menopausal hormone use and incident ovarian cancer (n=426) in 92601 post-menopausal women enrolled in the National Institutes of Health-AARP (NIH-AARP) Diet and Health Study. Participants were administered questionnaires in 1996-1997 and followed through 2006. Hazard rate ratios (RR) and 95% confidence intervals (CIs) were estimated using Cox regression.
Results: Increased risks were associated with long duration (10+ years) use of unopposed oestrogen (RR 2.15, 95% CI: 1.30-3.57 among women with a hysterectomy) and oestrogen plus progestin (RR 1.68, 95% CI: 1.13-2.49 among women with intact uteri) therapy. Similar risks were associated with progestins that were used sequentially (<15 days progestin per month) (RR 1.60, 95% CI: 1.10-2.33) or continuously (>25 days progestin per month) (RR 1.43, 95% CI: 1.032-2.01; P-value for heterogeneity=0.63).
Conclusion: Our findings suggest that long duration use of both unopposed estrogens and oestrogen plus progestins are associated with increased risks of ovarian cancer, and that risk associated with oestrogen plus progestin use does not vary by regimen (sequential or continuous).