Objectives: We compared the risk of cancer recurrence and all-cause mortality among users and nonusers of estrogen replacement therapy (ERT) after the diagnosis of breast cancer.
Study design: This was a systematic review of original research. Eligible studies were reviewed by 2 investigators who independently extracted data from each study according to a predetermined form and assessed each study for validity on standard characteristics. Meta-analyses were performed with Review Manager 4.1 to provide a summary of relative risks of cancer recurrence and mortality.
Population: Studies included 717 subjects who used hormone replacement therapy (HRT) at some time after their diagnosis of breast cancer, as well as 2545 subjects who did not use HRT.
Outcomes measured: Outcomes included breast cancer recurrence and all-cause mortality.
Results: Nine independent cohort studies and one 6-month pilot randomized controlled trial were identified. Studies were of variable quality. Breast cancer survivors using ERT experienced no increase in the risk of recurrence compared with controls (relative risk, 0.72; 95% confidence interval, 0.47-1.10) and had significantly fewer deaths (3.0%) than did the nonusers (11.4%) over the combined study periods (relative risk, 0.18; 95% confidence interval, 0.10-0.31). All tests for heterogeneity were nonsignificant.
Conclusions: Although limited by observational design, existing research does not support the universal withholding of ERT from well-informed women with a previous diagnosis of low-stage breast cancer. Long-term randomized controlled trials are needed.