Sex steroids and breast density predict breast cancer risk

Both circulating sex steroid levels and mammographic density are strong and independent predictors of breast cancer risk in postmenopausal women, according to the results of a nested case-control study.

Using a cohort of 253 women with breast cancer and 520 controls within the Nurses' Health Study, researchers found that women in the highest quartile for mammographic density had almost four times the risk for breast cancer as women in the lowest quartile (RR 3.8; 95% CI, 2.2–6.6; P_trend<0.001). Adjusting the analysis for circulating estradiol or circulating testosterone made little change (RR 3.9; 95% CI, 2.2–6.0; P_trend<0.001; and RR 4.1; 95% CI, 2.3–7.2, P_trend<0.001, respectively). Women with high levels of circulating estradiol or circulating testosterone had about twice as high a risk for developing breast cancer as women with low levels, before and after adjustment for mammographic density (RR 2.4; 95% CI, 1.4–4.0; and RR 2.0; 95% CI, 1.2–3.1, respectively). Women who had both high levels of plasma testosterone and very dense breasts were at six times the risk for breast cancer as women in the lowest tertiles for both (RR 6.0; 95% CI, 2.6–14.0). Figures were similar for women with both high circulating estradiol and mammographic density (RR 4.1; 95% CI, 1.7–9.8).

Tamimi RM, Byrne C, Colditz GA, et al. Endogenous hormone levels, mammographic density, and subsequent risk of breast cancer in postmenopausal women. J Natl Cancer Inst. 2007;99:1178-1187.