Menstrual and reproductive history, postmenopausal hormone use, and risk of benign proliferative epithelial disorders of the breast: a cohort study.

Menstrual and reproductive history and postmenopausal hormone use are well-established risk factors for breast cancer. However, previous studies that have assessed these factors in association with risk of benign proliferative epithelial disorders (BPED) of the breast, putative precursors of breast cancer, have yielded inconsistent findings. To investigate these associations, we conducted a cohort study among 68,132 postmenopausal women enrolled in the Women's Health Initiative randomized clinical trials. Women were prospectively followed and those reporting an open surgical biopsy or a core needle biopsy had histological sections obtained for centralized pathology review. Over an average of 7.8 years of follow-up, we identified 1,792 women with BPED of the breast. We used Cox proportional hazards models to estimate hazard ratios (HRs) and 95% confidence limits (CLs) for the associations of interest. Menstrual and reproductive histories were not associated with risk of BPED of the breast, overall or by histological subtype. Women who had used postmenopausal hormones for 15 years or more had a two-fold increase in risk of BPED of the breast compared to women who had never used postmenopausal hormones (HR = 2.03 95% CL = 1.73, 2.38) and the increase in risk was observed for both BPED of the breast without atypia and for atypical hyperplasia. Furthermore, the risk of BPED of the breast decreased with time since cessation of use so that there was essentially no increase in risk 5 or more years after ending use (HR for stopping >or=5 years earlier = 0.96, 95%CL = 0.79, 1.16; HR for stopping <5 years earlier = 1.32, 95% CL = 1.08,1.61).