miRNAs as potential markers for breast cancer and regulators of tumorigenesis and progression (Review).

Breast cancer (BC) is one of the most common malignancies affecting women. BC is a heterogeneous disease that involves multiple oncogenic pathways and/or genetic alterations. MicroRNAs (miRNAs or miRs) are a type of small endogenous single‑stranded RNA that pairs with the 3'untranslated region of target mRNAs to negatively regulate the gene expression of specific mRNA targets. miRNAs are thus involved in various cellular processes, including proliferation, differentiation, apoptosis, migration, metabolism and the stress response. Over the past decade, a number of studies have demonstrated that the expression levels of miRNAs are dysregulated in a number of types of cancer, including BC. In the present review, recent research on miRNAs involved in the occurrence and development of BC, as well as the current findings on miRNAs as potential biomarkers for BC are summarized. In addition, the association between miRNA dysregulation and BC development, and the current status of BC treatment and prognosis are discussed. Finally, several signaling pathways involved in the development of BC and the potential roles of miRNAs in these pathways are reviewed. The present review aims to provide insight into the roles of miRNAs in BC.