Postmenopausal women with relatively high serum concentrations of estrogen and testosterone have about twice the risk of developing breast cancer as women with relatively low serum concentrations of these sex hormones. Associations between serum sex hormone levels and risk of developing breast cancer were not different in women who donated blood closer in time to diagnosis, indicating higher hormone levels in these women were not a preclinical finding.
In each of the nine cohorts included in the analysis, women who donated blood were followed for an average of 2 to 10years. During that time 763 women developed breast cancer. Hormones in their blood were compared with the hormones of 1,567 women who were the same age when blood was donated as the women who developed breast cancer.
The results are highly statistically significant and were not altered when the researchers adjusted for established risk factors for breast cancer.