Hormone replacement therapy has been shown to reduce colorectal cancer incidence, but its effect on colorectal cancer mortality is controversial. The objective of this study was to determine the effect of hormone replacement therapy on survival from colorectal cancer.We performed a secondary analysis of data from the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, a large multicenter randomized trial run from 1993 to 2001, with follow-up data recently becoming mature. Participants were women aged 55 to 74 years, without recent colonoscopy. Data from the trial were analyzed to evaluate colorectal cancer incidence, disease-specific mortality, and all-cause mortality based on subjects' use of hormone replacement therapy at the time of randomization: never, current, or former users.A total of 75,587 women with 912 (1.21%) incident colorectal cancers and 239 associated deaths were analyzed, with median follow-up of 11.9 years. Overall, 88.6% were non-Hispanic white, and 10% had not completed high school. The never-user group was slightly older than the current or former user groups (average, 63.8 vs. 61.4 vs. 63.3 years; P .001). Almost one-half (47.1%) of the current users had undergone hysterectomy, compared with 21.6% of never-users and 34.0% of former users (P .001). Adjusted colorectal cancer incidence in current users compared to never-users was lower (hazard ratio [HR], 0.81; 95% confidence interval [CI], 0.69-0.94; P = .005), as was death from colorectal cancer (HR, 0.63; 95% CI, 0.47-0.85; P = .002) and all-cause mortality (HR, 0.76; 95% CI, 0.72-0.80; P .001).Hormone replacement therapy is associated with a reduced risk of colorectal cancer incidence and improved colorectal cancer-specific survival, as well as all-cause mortality.
