Hormone replacement therapy and the risk of death from breast cancer: A systematic review

OBJECTIVE: Recent studies have shown an increased relative risk of breast cancer with hormone replacement therapy for greater than or equal to5 years. However, tumors in hormone replacement therapy users are more likely to be localized and of a favorable histologic condition. Our objective was to determine the effects of hormone replacement therapy on the risk of death from breast cancer. STUDY DESIGN: We searched the literature to identify studies that addressed hormone replacement therapy and breast cancer death among healthy hormone replacement therapy users compared with nonusers. We included randomized controlled trials and cohort and case-control studies with adequate controls and retrievable risk estimates. RESULTS: Ten observational studies met the inclusion criteria; these studies varied widely with regard to population, choice of control group, ascertainment of exposure and outcome, and adjustment for potential confounders. CONCLUSION: Most studies showed a reduced risk of death from breast cancer in hormone replacement therapy users compared with nonusers. In a few studies, this risk reduction was attenuated after prolonged use or prolonged duration of follow-up. Limited information on recency of use, dose, or use of combined hormone replacement therapy was available.