Abstract P3-10-05: Normal breast biopsies reveal an "active" transcriptome associating with higher breast cancer risk (Gail) scores and increased IGF-1 growth factor expression
Authors: Benz C , Yau C , Benz S , Krings G , Powell M 
Published: February 2018

Background: Recent studies have identified at least two different transcriptional subtypes of benign human breast tissue (Haakensen et al., 2011), including an “active” subtype associated with increased risk of later life mortality from breast cancer (Troester et al., 2016). However, previous studies used "normal" breast samples from cosmetic surgery, biopsies from abnormal mammograms, or cancer-adjacent tissue. The present study evaluates normal breast transcriptome phenotypes from healthy women who donated for this study purpose only.

Methods: 200 formalin-fixed paraffin-embedded (FFPE) breast tissue biopsy samples were analyzed from healthy, parous non-Hispanic white women ranging in age from 27–66 (median = 45) with no prior history of breast cancer (&lt;16% had prior breast biopsies), who donated to the Komen Tissue Bank (KTB) and provided questionnaire data enabling calculation of breast cancer risk (Gail) scores. Extractable RNA from FFPE sections sufficient for RNA sequencing (˜100ng) was obtained from 145/200 donor samples; digitized H&E analysis confirmed normal breast histology. Transcript levels were quantified using RSEM and normalized; 2558 genes were used for unsupervised hierarchical clustering to identify “active” vs. “inactive” normal transcriptome subtypes as previously described (Roman-Perez et al., 2012), and these subtypes were compared for risk scores and IGF1R and IGF-1 gene expression levels and their respective signatures (Creighton et al., 2008; Mu et al., 2012).

Results: As expected, the normal histologic composition of these KTB samples varied considerably with mean % adipose area twice that of fibrous area, and epithelial content averaging &lt;5%. Unsupervised gene expression analysis produced two primary clusters, with 31% of donor samples showing the “active” transcriptome phenotype. These “active” breast samples came from women with significantly higher Gail scores (Wilcoxon rank sum p=0.007) and showed significantly different expression levels in 12 of 17 IGF-1/IGF1R pathway genes (FDR-corrected p values) including higher IGF-1, IGF-2, IRS1, IRS2, IGF2R, IGFBP3, IGFBP5, IGFBP6, and IGF2BP3 levels, and lower IGF1R, IGFBP2, and IGFBP3 transcript levels. A multigene signature associated with IGF-1 induction was consistent with the 2-fold significant increase in mean IGF-1 mRNA levels seen in this “active” subset; likewise, an independent multigene signature associated with IGF1R activation was consistent with the 0.84-fold significant reduction in mean IGF1R mRNA levels observed in this same subset.

Conclusion: Over 30% of healthy adult women with histologically normal breast tissue carry an “active” breast transcriptome phenotype previously linked to co-existent breast cancer and now shown to be associated with increased future risk of developing breast cancer assessed by Gail score. This “active” transcriptome phenotype is characterized by increased endogenous IGF-1 activity, a known breast cancer promoting growth factor, along with an inverse reduction in IGF1R expression and activity as previously seen in some breast cancers. Further morphologic and molecular characterization of this risk-associated subset of normal breast tissues is underway.

Citation Format: Benz C, Yau C, Benz S, Krings G, Powell M. Normal breast biopsies reveal an "active" transcriptome associating with higher breast cancer risk (Gail) scores and increased IGF-1 growth factor expression [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-10-05.