Abstract P3-08-20: The normal breast Active transcriptome associated with future breast cancer risk is driven by a dysregulated adipocyte microenvironment

Background: Previous studies of breast samples from cosmetic surgeries, benign biopsies associated with abnormal mammograms or cancer-adjacent tissue have identified at least two different transcriptional phenotypes of “normal” human breast tissue (Troester, 2009; Haakensen, 2011), including an “Active” phenotype linked to increased risk of later breast cancer mortality (Roman-Perez, 2012; Troester, 2016). This study compares breast histology and transcriptional phenotypes from healthy parous women with no prior history of breast disease who donated breast core biopsies for research and supplied reproductive histories enabling breast cancer risk calculation. Since the Active transcriptome phenotype was recently associated with increased mammary adipocyte content, we focused on the possibility that adipocyte activation contributes to the Active transcriptome and drives breast cancer risk. Methods: RNA from paraffin-embedded tissue sections sufficient for RNAseq analysis (~100ng) was extracted from 151/200 core biopsies donated to the Komen Tissue Bank by healthy, parous white women (age range: 27-66, median = 45) with no history of breast cancer. Questionnaire data enabled breast cancer risk (Gail) score calculation; and digitized H&E images were used for histologic analyses. A previously validated classifying signature was used in unsupervised hierarchical clustering to identify samples with Active (78/151) vs. Inactive (73/151) transcriptome phenotypes for comparison with donor risk factors, breast tissue composition, and expression of candidate genes and gene signatures. Results: Mean (+/-SD) BMI and Gail score values were 29.60 (+/-7.92) and 1.27 (+/- 1.34), respectively; BMI scores were not significantly different by phenotype, but Gail scores were significantly higher for donors with an Active phenotype (1.46 vs. 1.18; p=0.007, Wilcoxon rank-sum). Active normal breast tissue samples possessed significantly more (%) adipocyte nuclei (p=3.9e-11) and greater adipocyte size (p80% of this donor cohort would not qualify for breast cancer chemoprevention, those with Active transcriptomes had significantly higher Gail scores supporting their increased future risk for breast cancer development. The Active breast transcriptome is strongly associated with increased adipocyte content, size, and overexpression of signatures and genes (including those previously linked to breast cancer progression) indicating a differentially activated adipocyte population. This dysregulated mammary adipocyte microenvironment not only appears to underlie the Active transcriptome phenotype but also precedes and potentially predicts the future histologic development of breast cancer. Citation Format: Christopher C Benz, Taekyu Kang, Christina Yau, Chris Wong, Yulia Newton, Charlie Vaske, Stephen C Benz, Gregor Krings, Roman Camarda, Jill E Henry, Josh Stuart, Mark Powell. The normal breast Active transcriptome associated with future breast cancer risk is driven by a dysregulated adipocyte microenvironment [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 P3-08-20.