Reproductive history, use of exogenous hormones, and risk of colorectal adenomas.

Evidence suggests a role for reproductive and hormonal factors in the etiology of colorectal cancer. Investigation of adenomas, the presumed precursors of cancer, and reproductive characteristics may place such associations within a particular stage of carcinogenesis. We examined parity, age at first birth, age at menopause, and age at menarche as well as contraceptive and noncontraceptive hormone use in a case-control study of 347 women (115 cases with adenomas and 232 controls) conducted in North Carolina. Using unconditional logistic regression analysis, increasing age at menopause was found to be associated with a reduction in the risk of adenomas [odds ratio (OR), 0.26; 95% confidence interval (CI), 0.10-0.68]. An increased risk for adenomas was found for women undergoing surgical menopause as compared with women undergoing natural menopause (OR, 2.10; 95% CI, 1.05-4.21). Our results suggest a reduced risk of adenomas associated with noncontraceptive hormone use that was limited to a subgroup of women with natural menopause or bilateral oophorectomy (OR, 0.39; 95% CI, 0.15-0.97). No associations were seen between other reproductive characteristics and adenomas. These results suggest protective effects for both endogenous and exogenous female hormones that operate early in the process of carcinogenesis. Alternatively, lifestyle factors or other correlates of exogenous hormone use and delayed menopause could play a role in reduced adenoma risk.