Abstract 1158: Hormone gene expression and mammographic breast density in postmenopausal women
Authors: Mintz Rachel L. , Wang Mei , Xu Shuai , Markovic Chris , Toriola Adetunji T. 
Published: September 2020

Abstract
Introduction: Mammographic breast density (MBD), which reflects the amount of epithelial and stromal tissues relative to adipose tissue in the breast, is a strong risk factor for breast cancer. MBD declines with menopause, highlighting the role of endogenous hormones. Nevertheless, studies evaluating the associations of circulating hormone levels with MBD report conflicting results. Only a limited number of studies have addressed the genomic signatures of MBD, which may better capture the broader transcriptional changes associated with MBD and more accurately quantify hormonal exposure than circulating hormone levels. We therefore investigated the associations of hormonal gene expression with MBD in postmenopausal women.
Methods: We recruited 368 mid-life postmenopausal women (ages 50-64 years) who had annual screening mammogram at Washington University School of Medicine, St. Louis, MO between October 2017 and September 2018. Each participant completed a blood draw and a questionnaire on breast cancer risk factors. We used Volpara software to measure volumetric percent density (VPD, %), dense volume (VD, cm3) and non-dense volume (NDV, cm3). Prolactin (PRL), progesterone (PGR), estrogen receptor 1 (ESR1), signal transducer and activator of transcription (STAT1), and STAT5 gene expression were measured in total RNA isolated from plasma using NanoString nCounter system. Statistical analyses were performed with the NanoString nSolver Analysis Software. Fold changes in gene expression and p-values were calculated using nCounter default settings. Analyses were adjusted for body mass index (BMI), age, age at menarche, parity/age at first birth, race, and menopausal hormone use. VPD, DV, and NDV were log10 transformed to ensure the normality of the residuals.
Results: The mean age of study participants was 57.9 years. The mean BMI was 31.3kg/m2. The average VPD, DV, and NDV were 6.2%, 121.2 cm3, and 2134.4 cm3, respectively. There were strong correlations between STAT1 and STAT5 gene expression (r=0.59, p-value&lt;0.0001), and moderate correlations between ESR1 and PGR gene expression (r=0.43, p-value&lt;0.0001). ESR1 gene expression was associated with VPD, while PGR and STAT5 were marginally associated with NDV. One unit increase in ESR1 gene expression was associated with a 29% (95% CI 2-64%) increase in VPD (p-value=0.03). One unit increase in STAT5 gene expression was associated with an 8% (p-value=0.05) increase in NDV, while one unit increase in PGR gene expression was associated with a 20% (p-value=0.06) decrease in NDV. Hormone gene expression was not associated with DV.
Conclusions: We provide novel data on the associations of endogenous hormone gene expression with MBD in postmenopausal women. Future studies characterizing transcriptomic changes in hormone signaling and MBD are needed, as targeting these pathways could be used to reduce MBD for breast cancer prevention.
Citation Format: Rachel L. Mintz, Mei Wang, Shuai Xu, Chris Markovic, Adetunji T. Toriola. Hormone gene expression and mammographic breast density in postmenopausal women [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1158.