71P MicroRNA (miRNA) a putative biomarker to better define the molecular apocrine breast cancer (MABC) subtype

Abstract

Breast cancer (BC), is a heterogeneous disease, divided into molecular subtypes based on gene expression and clinical outcomes. MABC is a poorly diagnosed subtype, characterized by estrogen (ER), progesterone receptor (PR) negativity, and HER-2-amplification in most cases; yet it overexpresses androgen receptor (AR) and activates its pathway. Its improper diagnosis demands the adoption of complementary tools to refine classification; miRNA, key players in regulating cell behavior, AR, and tumorigenic processes of BC hold promise in defining and studying the behavior of MABC. 539 breast cancer microarray data were downloaded from The Cancer Genome Atlas (TCGA-BRCA). Cases with available miRNA data were retained and classified using citbcmst R package (PMID: 30289602). Differential expression analysis identified deregulated miRNAs using DEseq2. A validation set of 131 ER-neg samples was constituted and MABC tumors were characterized apart of triple-negative (TN)BC by the previously described molecular signature (AR, FOXA1 and AR-related genes, PMID: 23663520) on fresh tissue sections. Using miRCURY LNATM miRNA PCR assay, miRNA profiling was done for a panel of 6 differentially expressed miRNAs. Finally, expression of in silico predicted target genes of these miRNAs was assessed by RT-qPCR in MABC and TNBC cell lines after transfection with miRNA mimics. TCGA data analysis indicated MABC as a separate entity based on gene signature. MiRNA-seq data analysis depicted a set of 6 significantly deregulated miRNA with absolute value of log2 fold change> 1 and P-adjusted value <0.05 between MABC and TNBC. We validated on 78 MABC (27 HER2-/ 51 HER2+), and 53 TN samples, by miRNA profiling, significant upregulation of miR-2115-3p and miR-187-3p in MABC compared to TNBC. Preliminary data, showed that the overexpression of these miRNAs significantly downregulates in silico predicted target genes (FGF2, HMGCS1, and ADAM12) implicated in carcinogenesis differently in each of the models used. MABC has a unique signature of miRNA compared to TNBC. The identified miRNAs regulate a set of genes implicated in tumorigenic processes and can potentially serve as biomarkers to effectively diagnose, prognose and treat MABC