Plasma sex hormones and risk of conventional and serrated precursors of colorectal cancer in postmenopausal women.

<bold>Background: </bold>Sex hormones have been suggested to play a role in colorectal cancer (CRC), but their influence on early initiation of CRC remains unknown.<bold>Methods: </bold>We retrospectively examined the associations with risk of CRC precursors, including conventional adenomas and serrated polyps, for plasma estrone, estradiol, free estradiol, testosterone, free testosterone, sex hormone-binding globulin (SHBG), and the ratio of estradiol to testosterone among 5404 postmenopausal women from the Nurses' Health Study I and II. Multivariable logistic regression was used to calculate the odds ratio (OR) and 95% confidence intervals (CI). Given multiple testing, P < 0.005 was considered statistically significant.<bold>Results: </bold>During 20 years of follow-up, we documented 535 conventional adenoma cases and 402 serrated polyp cases. Higher concentrations of SHBG were associated with lower risk of conventional adenomas, particularly advanced adenomas (multivariable OR comparing the highest to the lowest quartile, 0.40, 95% CI 0.24-0.67, P for trend < 0.0001). A nominally significant association was found for SHBG with lower risk of large serrated polyps (≥ 10 mm) (OR, 0.47, 95% CI 0.17-1.35, P for trend = 0.02) as well as free estradiol and free testosterone with higher risk of conventional adenomas (OR, 1.54, 95% CI 1.02-2.31, P for trend = 0.03 and OR, 1.33, 95% CI 0.99-1.78, P for trend = 0.03, respectively).<bold>Conclusions: </bold>The findings suggest a potential role of sex hormones, particularly SHBG, in early colorectal carcinogenesis. [ABSTRACT FROM AUTHOR]