Prediagnostic Circulating Levels of Sex Steroid Hormones and SHBG in Relation to Risk of Ductal Carcinoma In Situ of the Breast among UK Women

Background: Sex steroid hormones and sex hormone-binding globulin (SHBG) have been implicated in the etiology of invasive breast cancer, but their associations with risk of the precursor lesion, ductal carcinoma in situ (DCIS) of the breast, remain unclear. Methods: We used Cox proportional hazards regression models to estimate the associations of serum levels of estradiol (premenopausal women only), testosterone, and/or SHBG with DCIS risk among 182,935 women. After a median follow-up of 7.1 years, 186 and 531 DCIS cases were ascertained in premenopausal and postmenopausal women, respectively. Results: Total and free estradiol were positively associated with risk of DCIS among premenopausal women. The HRs for the highest versus the lowest tertiles were 1.54 (1.06-2.23) and 1.72 [95% confidence interval (CI), 1.15-2.57], respectively. Among postmenopausal women, elevated levels of free testosterone (FT), and to a lesser extent, total testosterone, were positively associated with DCIS risk. The HRs for the highest versus the lowest quartiles were 1.42 (95% CI, 1.09-1.85) and 1.16 (95% CI, 0.91-1.48), respectively. Serum SHBG levels were inversely associated with risk of DCIS among postmenopausal women (HRq4 vs. q1: 0.75; 95% CI, 0.56-0.99). Conclusions: This study suggests that elevated levels of estradiol are associated with increased risk of DCIS among premenopausal women, and that among postmenopausal women, elevated levels of testosterone, and particularly those of FT, are associated with increased DCIS risk, while elevated levels of SHBG are associated with reduced risk. Impact: These findings may be helpful in developing prevention strategies aimed at reducing breast cancer risk among premenopausal and postmenopausal women.