Hormone replacement therapy and the risk of colorectal cancer: a meta-analysis

Objective: To review systematically the association between hormone replacement therapy and colorectal cancer incidence and mortality.Methods: We conducted a literature search of English-language studies using MEDLINE, Current Contents, CancerLit, and bibliographies of selected studies. The exposures of interest were ever, recent, or former use of hormone replacement therapy (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 usage as use either at time of assessment or within the previous year. Studies were evaluated independently by two of the authors. We included studies with adequate controls and retrievable risk estimates. We excluded letters, abstracts, and multiple publications of the same data. The most adjusted risk estimates were extracted. We used the empirical Bayes method, a random-effects model, to calculate summary relative risks (RR) and confidence intervals (CI).Results: Recent use of HRT was associated with a significantly decreased risk of colon cancer (RR = 0.69, 95% CI 0.58-0.81). Protection was limited to recent users; the risk of colon cancer with any use of HRT was 0.94 (95% CI 0.79-1.12). Duration of use was not significant. Three studies addressed colon cancer mortality; the summary RR for death from colon cancer in HRT users was 0.72 (95% CI 0.64-0.81). Rectal cancer incidence and mortality were not associated with HRT use.Conclusion: The risk of colon cancer may be decreased among recent postmenopausal HRT users. Although data are limited, the risk of death from colon cancer may also be lower in HRT users.