Objective: To review systematically the association between hormone replacement therapy (HRT) and the risk of developing or dying from colorectal cancer.
Data sources: We searched the English-language literature using MEDLINE, Current Contents, CancerLit, and bibliographies of selected studies.
Methods of study selection: We included studies that specifically addressed the association of HRT with colorectal cancer, had adequate controls, and had retrievable risk estimates. We excluded letters, reviews, and multiple publications of the same data.
Tabulation, integration, and results: Studies were evaluated independently by two of the authors. The exposures of interest were ever, recent, or former use of HRT, and the main outcome measures were colon and rectal cancer incidence and mortality. To reduce the risk of a "healthy estrogen user" bias, we defined recent HRT use as either at time of assessment or within the previous year. The most adjusted risk estimates were extracted. We used a random-effects model to calculate summary relative risks (RRs) and confidence intervals (CIs). Recent use of HRT was associated with a 33% reduction in the risk of colon cancer (RR = 0.67; 95% CI 0.59, 0.77). Protection was limited to recent users; the risk of colon cancer with ever use of HRT was 0.92 (95% CI 0.79, 1.08). Duration of use was not significant. Three studies addressed the risk of fatal colon cancer; the summary RR for death from colon cancer in HRT users was 0.72 (95% CI 0.64, 0.81) compared with nonusers. Rectal cancer incidence was not associated with HRT.
Conclusion: The risk of colon cancer may be decreased among recent postmenopausal HRT users. Although data are limited, the risk of fatal colon cancer also may be lower in HRT users.