Abstract P2-11-10: Estrogen drives the therapeutic hormonal response in ER+ breast cancers
Authors: Hugh Judith , Haddon Lacey , Githaka John Maringa , Hu Xiuying , Bigras Gilbert , Loney Brittney , Hanson John , Gabos Zsolt , Huang Fleur , Hitt Mary , McManus Kirk , Dabbs Kelly , Mackey John 
Published: March 2020

Abstract
Background: It is thought that estrogen induces proliferation in all estrogen receptor positive (ER+) breast cancer cells. However, there are paradoxical reports of a therapeutic effect of estrogen (E2) with possible E2 induced apoptosis in tumors that are chronically E2 deprived such as after the menopause. We tested whether E2 induced proliferation or apoptosis in post-menopausal women with newly diagnosed breast cancer.
Method: We treated 19 women with low dose estradiol (6mg/day) in a window of opportunity trial. Changes in Ki67 and the Prosigna™ Risk of Recurrence Score (ROR) were measured. 13 patients with sufficient tissue had whole transcriptome RNA-seq analysis on pre- and post-treatment specimens to test pathway induction and to derive a gene expression profile (GEP) associated with response to E2. 13 contemporaneous untreated patients were matched for surgical ROR scores to serve as post-hoc controls. The E2-response GEP was then tested on publicly available datasets of ER+ patients as well as ER transfected cell lines.
Results: Estradiol was well tolerated. 68% (13/19) and 62% (8/13) of tumors showed decreases in Ki67 and ROR respectively with the Ki67 decrease being significant (p=0.017) compared to control untreated tumors. Although the direction of change in the Ki67 and ROR indices showed good concordance (10/11, κ =0.74) the change in ROR was not statistically significant (p=0.064) because of the smaller sample size. We compared responders (ROR decrease &gt;2 Standard Deviation beyond controls) to non-responders (ROR and Ki67 changes closest to zero) and generated 3 GEPs: (i) 69 genes differentially activated by E2 (ii) 30 genes upregulated only in the pre-treatment biopsies of responders and (iii) 45 genes downregulated only in the post-treatment specimens of responders. A Reactome (https://reactome.org/) Pathway Analysis showed 17 of the top 20 pathways differentially activated by E2 were involved in the cell cycle with no activation of apoptosis pathways. Although 3 of the 36 genes characteristic of an E2-induced apoptotic response (Ariazi et al. Proc. Natl. Acad. Sci. 2011) had a significant fold change in Responders the Chi-square test was non-significant (p= 0.24) consistent with a non-apoptotic E2 response. Responders were found to have higher pre-treatment levels of ESR1 (Pearson R=0.504, p=0.04). E2 induced increases in the p21 gene (CDKN1A) were found in both E2 responsive patients (Pearson R=0.640, P = 0.009) and ER-transfected MCF-7 cells (p&lt;0.009), consistent with the induction of cell cycle blockade. Algorithmic combination of the biopsy and surgical GEP of the E2 responders predicted distant recurrence free survival in cohorts of patients who had been treated with Tamoxifen (Symmans et al. J Clin Oncology 2010) (p&lt;0.001) or Aromatase Inhibitors (Miller et al. J Clin Oncology 2009) (p&lt; 0.0001) but not in an untreated cohort (Symmans 2010).
Conclusions: These findings suggest that E2 can induce cell cycle blockade in some higher ER expressing ER+ tumors without activating apoptosis. In such patients, Tamoxifen may function as an E2 agonist. These data suggest that the estrogenic testosterone metabolite 5α-androstane-3β,17β-diol, an ERα agonist increased by aromatase inhibition, (Sikora et al. Breast Cancer Res Treat 2009) may contribute to the benefit from aromatase inhibitors. This represents a conceptual change of the biological action of E2 from pro-proliferative to anti-proliferative in some ER+ patients and suggests that i) E2 treatment may be a therapeutic option for selected post-menopausal ER+ patients, and ii) a single signature can predict which patients will have an anti-proliferative response to E2, tamoxifen, and aromatase inhibitors.
Citation Format: Judith Hugh, Lacey Haddon, John Maringa Githaka, Xiuying Hu, Gilbert Bigras, Brittney Loney, John Hanson, Zsolt Gabos, Fleur Huang, Mary Hitt, Kirk McManus, Kelly Dabbs, John Mackey. Estrogen drives the therapeutic hormonal response in ER+ breast cancers [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-11-10.