Levels of endogenous sex hormones are strongly associated with breast cancer risk in postmenopausal women.

In this collaborative analysis of the worldwide data on endogenous hormones and prostate cancer risk, serum concentrations of sex hormones were not associated with the risk of prostate cancer.

Background The relationships of circulating concentrations of oestrogens, progesterone and androgens with breast cancer and related risk factors in premenopausal women are not well understood. Methods Individual data on prediagnostic sex hormone and sex hormone binding globulin (SHBG) concentrations were contributed by 7 prospective studies. Analyses were restricted to women who were premenopausal and under age 50 at blood collection, and to breast cancer cases diagnosed before age 50. The odds ratios (ORs) with 95% confidence intervals (95% CIs) for breast cancer associated with hormone concentrations were estimated by conditional logistic regression in up to 767 cases and 1699 controls matched for age, date of blood collection, and day of cycle, with stratification by study and further adjustment for cycle phase. The associations of hormones with risk factors for breast cancer in control women were examined by comparing geometric mean hormone concentrations in categories of these risk factors, adjusted for study, age, phase of menstrual cycle and body mass index (BMI). All statistical tests were two-sided. Findings ORs for breast cancer associated with a doubling in hormone concentration were 1.19 (95% CI 1.06–1.35) for oestradiol, 1.17 (1.03–1.33) for calculated free oestradiol, 1.27 (1.05–1.54) for oestrone, 1.30 (1.10–1.55) for androstenedione, 1.17 (1.04–1.32) for dehydroepiandrosterone sulphate, 1.18 (1.03–1.35) for testosterone and 1.08 (0.97–1.21) for calculated free testosterone. Breast cancer risk was not associated with luteal phase progesterone (for a doubling in concentration OR=1.00 (0.92–1.09)), and adjustment for other factors had little effect on any of these ORs. The cross-sectional analyses in control women showed several associations of sex hormones with breast cancer risk factors. Interpretation Circulating oestrogens and androgens are positively associated with the risk for breast cancer in premenopausal women.