Relationship between plasma estradiol levels and estrogen-responsive gene expression in estrogen receptor-positive breast cancer in postmenopausal women

Abstract

PURPOSE To determine whether plasma estradiol (E2) levels are related to gene expression in estrogen receptor (ER)-positive breast cancers in postmenopausal women. Materials and METHODS Genome-wide RNA profiles were obtained from pretreatment core-cut tumor biopsies from 104 postmenopausal patients with primary ER-positive breast cancer treated with neoadjuvant anastrozole. Pretreatment plasma E2 levels were determined by highly sensitive radioimmunoassay. Genes were identified for which expression was correlated with pretreatment plasma E2 levels. Validation was performed in an independent set of 73 ER-positive breast cancers. Results The expression of many known estrogen-responsive genes and gene sets was highly significantly associated with plasma E2 levels (eg, TFF1/pS2, GREB1, PDZK1 and PGR; P < .005). Plasma E2 explained 27% of the average expression of these four average estrogen-responsive genes (ie, AvERG; r = 0.51; P < .0001), and a standardized mean of plasma E2 levels and ER transcript levels explained 37% (r, 0.61). These observations were validated in an independent set of 73 ER-positive tumors. Exploratory analysis suggested that addition of the nuclear coregulators in a multivariable analysis with ER and E2 levels might additionally improve the relationship with the AvERG. Plasma E2 and the standardized mean of E2 and ER were both significantly correlated with 2-week Ki67, a surrogate marker of clinical outcome (r = -0.179; P = .05; and r = -0.389; P = .0005, respectively). CONCLUSION Plasma E2 levels are significantly associated with gene expression of ER-positive breast cancers and should be considered in future genomic studies of ER-positive breast cancer. The AvERG is a new experimental tool for the study of putative estrogenic stimuli of breast cancer.

Fig 1.

Correlation of plasma estradiol and estrogen-responsive gene expression. (A) Plasma estradiol versus TFF1 expression in discovery data set. (B) Plasma estradiol versus GREB1 expression in discovery data set. (C) Plasma estradiol versus AvERG (average estrogen-responsive genes; ie, mean of TFF1, GREB1, PDZK1, and PGR) expression in discovery data set. (D) Plasma estradiol versus AvERG expression in independent validation data set.

Fig 2.

Map showing relationship between genes positively correlated with plasma estradiol superimposed on Ingenuity map. Pathway analysis was carried out on 98 positively correlated genes (P < .005), and functional annotation revealed a network of 29 genes related through known estradiol- and progesterone-related signaling pathways. Genes correlated with plasma estradiol are shown in red, and the intensity of red coloration reflects the degree of correlation.

Fig 3.

(A) Standardized mean of plasma estradiol and ESR1 expression versus AvERG (average estrogen-responsive genes; ie, mean of TFF1, GREB1, PDZK1, and PGR) expression in discovery data set. (B) Standardized mean of plasma estradiol and ESR1 expression versus AvERG expression in independent validation data set.

Fig 4.

Standardized mean of plasma estradiol and ESR1 expression versus Ki67 percentage staining 2 weeks after anastrozole treatment.