RESUMEN
Breast cancer is the second most common malignancy diagnosed in women, supporting the need for identification of novel prognostic and diagnostic biomarkers. Recently, microRNAs have emerged as molecular regulators that can have key roles in pathogenesis and progression of different malignancies, including breast cancer. Micro-RNAs can be circulated in body fluid, suggesting their values as non-invasive marker. There is growing body of evidence showing the aberrant activation of some known circulating miRNAs, for example let-151a, miR-21, miR-155, miR-,145 miR-18a, miR-16 as well as tissue specific-miRNAs, for example miR-182, miR-145, miR-21, miR-155/154, miR-203, miR-213, miR-7 in patients affected by breast cancer. In addition, there is growing body of evidences on the value of miRNAs to be associated with drug-resistance, suggesting their values as a potential approach to overcome chemo-resistance. Attuned with these facts, this review highlights recent preclinical and clinical investigation performed on tissue-specific miRNAs and circulating as novel promising biomarkers for detection of patients at early stages, prediction of prognosis, and monitoring of the patients in response to therapy.