The Role of MicroRNAs in the Chemoresistance of Breast Cancer.

Preclinical Research Breast cancer is the most prevalent malignancy in women with more than 1.3 million new cases every year worldwide. Chemotherapy is a critical therapeutic strategy for breast cancer, while chemoresistance remains a major obstacle to treatment success. In the past two decades, significant progress has been achieved in understanding drug resistance in breast cancer, involving drug efflux, alterations in DNA repair pathways, suppression of apoptosis as well as epithelial-mesenchymal transition, and cancer stem cells. However, more effective therapeutic targets and novel biomarkers are still urgently needed to improve the overall survival and refine the therapeutic strategy for breast cancer patients. MicroRNAs (miRNAs) play crucial roles in cellular processes, such as cell differentiation, proliferation, and apoptosis. The recent discovery of miRNAs in malignancy has provided new directions for research on mechanisms underlying response to chemotherapy. Furthermore, several studies have documented that selected miRNAs, such as miR-200c and miR-34a, may influence response to chemotherapy in several tumor types, including breast cancer. The use of miRNAs as therapeutic targets to overcome chemoresistance is currently under investigation. In this review, we summarize the roles of miRNAs in chemoresistance through multiple molecular mechanisms, and highlight the potential diagnostic and therapeutic applications of miRNAs in overcoming breast cancer chemoresistance.