Key microRNAs in the biology of breast cancer; emerging evidence in the last decade.

microRNAs (miRNAs) are a family of small noncoding RNAs that play a pivotal role in the regulation of main biological and physiological processes, including cell cycle regulation, proliferation, differentiation, apoptosis, stem cell maintenance, and organ development. Dysregulation of these tiny molecules has been related to different human diseases, such as cancer. It has been estimated that more than 50% of these noncoding RNA sequences are placed on fragile sites or cancer-associated genomic regions. After the discovery of the first specific miRNA signatures in breast cancer, many studies focused on the involvement of these small RNAs in the pathophysiology of breast tumors and their possible clinical implications as reliable prognostic biomarkers or as a new therapeutic approach. Therefore, the present review will focus on the recent findings on the involvement of miRNAs in the biology of breast cancer associated with their clinical implications.