Objective: High levels of sex steroid hormones and prolactin have been suggested to enhance breast cancer development. Low levels of SHBG may indicate high levels of (bio-available) steroid hormones. The present study investigates whether high levels of sex steroid hormones and prolactin, and/or low levels of SHBG, are associated with high breast cancer risk.
Methods: Blood samples were collected in about 65,000 women participating in two population-based prospective cohort studies in Sweden. Follow-up yielded 173 postmenopausal breast cancer cases who had not been exposed to HRT. Levels of estrone, estradiol, SHBG, FSH, prolactin, testosterone, androstenedione and DHEAs were analysed in cases and 438 controls. Logistic regression analysis yielded odds ratios (ORs), with 95% confidence intervals, adjusted for potential confounders.
Results: The risk of breast cancer was associated with the highest versus lowest quartiles of estrone, OR: 2.58 (1.50-4.44), estradiol (dichotomised: high versus low) (1.73: 1.04-2.88), and testosterone (1.87: 1.08-3.25). High risks, although not statistically significant, were seen for androstenedione (1.58: 0.92-2.72) and DHEAs (1.62: 0.89-2.72). No strong associations were seen between SHBG or prolactin and risk of breast cancer.
Conclusions: High levels of estrone, estradiol, testosterone, and possibly androstenedione and DHEAs, in postmenopausal women are associated with a high risk of subsequent breast cancer.