A new study has reported that circulating estradiol levels are positively associated with gene expression in estrogen receptor positive (ER+) breast cancer in postmenopausal women. The authors evaluated genome-wide RNA profiles from pretreatment tumor biopsies of 104 postmenopausal patients with primary ER+ breast cancer. Pretreatment estradiol levels were determined with a blood test and genes were identified for which expression was associated with estradiol levels.

The expression of many known estrogen-responsive genes and gene sets was found to be highly significantly associated with circulating estradiol levels. Plasma estradiol level explained 27% of the average expression of four specific estrogen-responsive genes. Furthermore, a measure using a standardized average of plasma estradiol levels and estrogen receptor transcript levels explained 37% of gene expression. Plasma estradiol and the standardized mean of estradiol and estrogen receptor were both found to be significantly correlated with two-week Ki67, a proliferation index which is associated with prognosis. The authors conclude that plasma estradiol levels are significantly associated with gene expression of ER+ tumors.