Menopausal hormone therapy and risk of colorectal cancer

B119

Menopausal hormone therapy has been associated with a reduced risk of colorectal cancer. However, few studies have investigated colorectal cancer risk by menopausal hormone therapy formulation (i.e., unopposed estrogen versus estrogen plus progestin) or regimen (i.e., sequential versus continuous estrogen plus progestin use). We evaluated colorectal cancer risk associated with duration and recency of specific menopausal hormone therapy formulations and regimens using a large, prospective study of 56,733 postmenopausal women who were participants of the Breast Cancer Detection Demonstration Project (BCDDP) follow-up study. Time-dependent hormone therapy use and other risk factors were ascertained through telephone interviews and three mailed questionnaires between 1979 and 1998. The final colorectal cancer group included 960 women who were identified from self report, medical records, state registry data, and the National Death Index. Poisson regression was used to generate multivariable rate ratios (RRs) and 95% confidence intervals (95% CI). Ever use of any menopausal hormone therapy was associated with a statistically nonsignificant reduced risk of colorectal cancer compared with never users (RR, 0.91; 95% CI, 0.80-1.04). There was a statistically significant decreased risk of colorectal cancer among ever-users of unopposed estrogen therapy compared with never users (RR, 0.83; 95% CI, 0.70-0.99). Among unopposed estrogen users, the largest reduced risk was observed for current users (RR, 0.75; 95% CI, 0.54-1.05) and users of ten or more years duration (RR, 0.74; 95% CI, 0.56-0.96). We found a statistically nonsignificant reduced risk among users of estrogen plus progestin therapy (RR, 0.78; 95% CI, 0.60-1.02), with sequential regimen users (progestin <15 days per cycle) having the largest risk reduction (RR 0.64; 95% CI, 0.43-0.95). Among estrogen plus progestin users, past users of five or more years ago (RR, 0.55; 95% CI, 0.32-0.98) and users of medium duration of two to five years (RR, 0.52; 95% CI, 0.32-0.87) had the largest reduction in risk, regardless of combination therapy regimen. In this study, estrogen plus progestin use, especially sequential regimen use, was associated with the largest reduction of colorectal cancer risk.