The expression of microRNAs (miRNAs) in a tissue- and development-specific manner has indicated that they play an essential role in the maintenance of biological homeostasis. In cancer, the deregulation of these small non-coding RNA molecules modulates the expression of numerous tumor-associated genes and cellular processes. The high levels of cancer-associated sensitivity and specificity of plasma/serum and exosomal miRNA profiles reflect disease development, tumor load, malignant progression towards metastatic relapse and drug resistance. The present review focuses on the findings related to the expression and function of miRNAs in breast cancer, and discusses the potential clinical uses of miRNAs, including their roles as therapeutic targets and diagnostic markers.
