Molecular portraits of mammographic breast density in normal breast tissue

Abstract

22227 Background: High mammographic density is associated with a 6-fold increased risk of breast cancer. Pathways responsible for this increased density are unknown. We hypothesize that specific molecular pathways exist that are associated with increased mammographic density and breast cancer risk. Methods: Histologically confirmed normal breast tissue was collected from women undergoing breast surgery who had available demographic data and mammograms for review. Breast parenchymal density was classified according to the American College of Radiology's Breast Imaging - Reporting and Data System reporting system. Quantitative classification of mammographic parenchyma was performed using thresholding method and percent density. Women with low (less than 50%) versus high (greater than 50%) breast density were compared. Double-stranded cDNA was synthesized from the normal breast tissue using an oligo-dT primer containing a T7 RNA polymerase promoter, followed by in vitro transcription with biotinylated ribonucleotides. The labeled cRNA was hybridized to Affymetrix HG U133Plus2 chips which comprise ∼28,600 genes to determine gene expression patterns. Results: Sixty-two women were identified, 26 (42%) had high, and 36 (58%) had low mammographic density. Neither menopausal nor hormone receptor status influenced the gene expression pattern. 841 genes had differential expression between normal breast tissue with high and low mammographic density (p<0.01, fold change >1.2) and had a low false discovery rate (<10%). Of these 841 differentially expressed genes, the most significant canonical pathways up-regulated in dense normal breast tissue included the Notch (DLK1), Wnt (FZD10), and insulin receptor growth signaling (IGFBP1), which are known regulators of normal mammary stem cell self-renewal. In addition, genes governing alternative splicing were increased, including a non-coding RNA (MALAT1, TncRNA), and RNA splicing factors (SFRS1, SFRS3 SFRS4, and SFRS7). Conclusions: Specific pathways, including those involved in normal stem cell self-renewal and with epigenetic regulation, may influence breast density and hence, breast cancer risk. Understanding these pathways could lead to early chemopreventive interventions in high-risk women. No significant financial relationships to disclose.