MicroRNAs and drug resistance of breast cancer: basic evidence and clinical applications.

Breast cancer is the most common malignancy and leading cause of cancer mortality in women. Drug resistance is a major obstacle in systemic therapy of breast cancer, which leads therapeutic failure, incontrollable disease, and mortality. MiRNAs are an emerging field in cancer research. Recent evidence demonstrates that miRNAs are core regulators in drug resistance of breast cancer. Preclinical research reveals that miRNAs modulate the multidrug-resistant signal transduction network through up-regulated drug efflux transporters and anti-apoptotic proteins, acquisition of epithelial-mesenchymal transition, and formation of cancer stem cells. MiRNAs mediate endocrine resistance through modulating ERα expression, receptor tyrosine kinase signaling, cell survival signaling, and apoptosis. Such emerging evidence indicates that miRNAs could be potential biomarkers for predicting a response to systemic therapy and prognosis in clinical settings. Targeting specific miRNAs of the drug-resistant network is promising in overcoming drug resistance in breast cancer.