Hormone replacement therapy after breast cancer: A systematic review and quantitative assessment of risk

Purpose: Hormone replacement therapy (HRT) is typically withheld from women with breast cancer because of concern that it might increase the risk of r ecurrence. The purpose of this study was to quantify the risk of recurrent breast cancer associated with HRT among breast cancer survivors. Methods: We performed a systematic literature review through May 1999, calc ulating the relative risk (RR) of breast cancer recurrence in each study by comparing the number of recurrences in the HRT group to those in the contr ol group. In studies that did not contain a control group, we constructed o ne by estimating the expected number of recurrences based on data from the Early Breast Cancer Trialists' Collaborative Group, adjusting for nodal sta tus and disease-free interval. RRs across all studies were combined using r andom-effects models. Results: Of the 11 eligible studies, four had control groups and included 2 14 breast cancer survivors who began HRT after a mean disease-free interval of 52 months. Over a mean follow-vp of 30 months, 17 of 214 HRT users expe rienced recurrence (4.2% per year), compared with 66 of 623 controls (5.4% per year). HRT did not seem to affect breast cancer recurrence risk (RR = 0 .64, 95% confidence interval [CI], 0.36 to 1.15). including all 11 studies in the analyses (669 HRT users), using estimated control groups for the sev en uncontrolled trials, the combined RR was 0.82 (95% CI, 0.58 to 1.15). Conclusion: Although our analyses suggest that HRT has no significant effec t on breast cancer recurrence, these findings were based on observational d ata subject to a variety of biases. (C) 2001 by American Society of Clinica l Oncology.