Background: Accumulating evidence suggests that postmenopausal hormone use may decrease the risk for colorectal cancer.
Objective: To examine the relation of postmenopausal hormone therapy to colorectal adenoma and cancer.
Design: Prospective cohort and nested case-control studies.
Setting: Nurses' Health Study, a study of registered nurses recruited from 11 U.S. states.
Participants: 59 002 postmenopausal participants in the Nurses' Health Study.
Measurements: Self-reported data on hormone use and cases of distal colorectal adenoma and colorectal cancer obtained from biennial questionnaires completed from 1980 to 1994. Cases of colorectal adenoma and cancer were confirmed by medical record review.
Results: 470 women developed colorectal cancer, and 838 developed distal colorectal adenomas. Current use of postmenopausal hormones was associated with a decreased risk for colorectal cancer (relative risk [RR], 0.65 [95% CI, 0.50 to 0.83]). This association was attenuated in past users (RR, 0.84 [CI, 0.67 to 1.05]) and disappeared 5 years after hormone use was discontinued (RR, 0.92 [CI, 0.70 to 1.21]). Longer duration of current use did not afford greater protection (RR with > or =5 years of use, 0.72 [CI, 0.53 to 0.96]). Even after exclusion of women who reported having screening sigmoidoscopy, the relative risk for colorectal cancer seen with current hormone use was 0.64 (CI, 0.49 to 0.82). This suggests that the apparent protection is unlikely to be due to more intensive screening among hormone users. Current users also had a lower risk for large (> or =1 cm) adenomas than did women who had never used hormones (RR, 0.74 [CI, 0.55 to 0.99]), although no overall material association was seen between colorectal adenoma and current hormone use (RR, 0.91 [CI,0.77 to 1.08]).
Conclusions: The risk for colorectal cancer was decreased among women currently receiving postmenopausal hormone therapy, but the apparent reduction substantially diminished upon cessation of therapy. Hormone use was inversely associated with large colorectal adenomas but not small ones.