The interaction of age and hormone replacement therapy on colon adenoma risk

Background: Several studies have identified a possible interaction between age and hormone replacement therapy on colon neoplasm risk. We re-evaluated this interaction and determined if this interaction may be explained by the longer duration of estrogen use in older, rather than younger, women. Methods: Included in the case-control study were 755 women (169 cases and 586 controls.) who were recruited from patients with no prior history of colorectal neoplasm and undergoing an elective colonoscopy examination. Results: There was a significant interaction between age and hormone replacement therapy use (P = 0.03) with current estrogen users who were over 56 years of age having a reduced odds of colon adenoma (OR, 0.40; 95% CI, 0.16–0.98) when compared to never users. Both older women who had used hormone replacement therapy for 3 or less years (OR, 0.07; 95% CI, 0.006–0.81) and those reporting greater than 10 years of use (OR, 0.27; 95% CI, 0.09–0.80) had a reduced adjusted odds for adenomas when compared to non-users. No apparent association with estrogen replacement therapy was found among younger women (<56 years). Conclusions: Duration of use is not likely to explain the stronger association of hormone replacement therapy use with colon neoplasm in older women. Additional work is needed to better characterize the underlying mechanisms associated with this interaction.