miRNA-135b in molecular characterization of triple-negative breast cancer (TNBC).

TNBC accounts for 12-24% of all mammary cancers (BC). Its clinical and genetic heterogeneity and the lack of unambiguous molecular targets contribute to the scarcity of therapeutic options for this BC variant. Recently, the BC molecular biology has entered in the era of microRNAs (miRNA), a class of small highly conserved regulatory endogenous non-coding RNAs, which control complicated signaling pathways, governing cell cycle, proliferation, differentiation, apoptosis, etc., and whose deregulation contributes to the tumour development. Our goal was to improve the knowledge of TNBC biology analyzing the miRNA expression profile and to identify new potential prognostic and predictive biomarkers. We conducted a human miRNome analysis by TaqMan Low Density Array comparing different TNBC subtypes, defined by immunohistochemical basal markers, such as epidermal growth factor receptor and cytokeratin 5/6. Quantitative reverse transcription polymerase chain reaction confirmed differential expression of miRNA. We identified a single miRNA signature given by miR-135b expression levels, which allowed the distinction of TNBC with and without basal-like phenotype. Our study sheds light on the molecular complexity of TNBC and shows for the first time that miR-135b expression is strictly related to TNBC basal-like molecular subtype, acting as an oncogene in the tumor pathogenesis.