Breast cancer(BC) is the most frequent type of non skin cancer among women and a major leading cause of cancer-related deaths in Western countries. It is substantial to discover novel biomarkers with diagnostic, prognostic or predictive usefulness as well as therapeutic value for BC. Micro-RNAs(miR NAs) belong to a novel class of endogenous interfering RNAs that play a crucial role in post transcriptional gene silencing through m RNA targeting and, thus, are involved in many biological processes encompassing apoptosis,cell-cycle control, cell proliferation, DNA repair, immunity, metabolism, stress, aging, etc. Mi RNAs exert their action mainly in a tumor suppressive or oncogenic manner. The specific aberrant expression patterns of miR NAs in BC that are detected with the use of highthroughput technologies reflect their key role in cancer initiation, progression, migration, invasion and metastasis. The detection of circulating extracellular miR NAs in plasma of BC patients may provide novel, non-invasive biomarkers in favor of BC diagnosis and prognosis and,at the same time, accumulating evidence has underscored the possible contribution of miR NAs as valuable biomarkers to predict response to chemotherapy or radiotherapy. Data from in vitro and in vivo studies on BC have revealed promising therapeutic approaches via mi RNA delivery and mi RNA inhibition. The purpose of this review is to explore the ontological role of miR NAs in BC etiopathogenesis as well as to highlight their potential, not only as non-invasive circulating biomarkers with diagnostic and prognostic significance, but also as treatment response predictors and therapeutic targets aiding BC management. Breast cancer (BC) is the most frequent type of non-skin cancer among women and a major leading cause of cancer-related deaths in Western countries. It is substantial to discover novel biomarkers with diagnostic, prognostic or predictive usefulness as well as therapeutic value for BC. Micro-RNAs (miR NAs) belong to a novel class of endogenous interfering RNAs that play a crucial role in post transcriptional gene silencing through m RNA targeting and, thus, are involved in many biological processes encompassing apoptosis, cell-cycle control, cell proliferation, DNA repair, immunity, metabolism, stress, aging, etc. Mi RNAs exert their action mainly in a tumor suppressive or oncogenic manner. The specific aberrant expression patterns of miR NAs in BC that are detected with the use of high throughput technology their key role in cancer initiation, progression, migration, invasion and metastasis. The detection of circulating extracellular miR NAs in plasma of BC patients may provide n ovel, non-invasive biomarkers in favor of BC diagnosis and prognosis and, at the same time, accumulating evidence has underscored the possible contribution of miR NAs as valuable biomarkers to predict response to chemotherapy or radiotherapy. Data from in vitro and in vivo studies on BC have revealed pre- sible approaches via miRNA delivery and mi RNA inhibition. The purpose of this review is to explore the ontological role of miR NAs in BC etiopathogenesis as well as to highlight their potential, not only as non-invasive circulating biomarkers with diagnostic and prognostic significance, but also as treatment response predictors and therapeutic targets aiding BC management.