miRNA clusters as therapeutic targets for hormone-resistant breast cancer.

MicroRNAs are small non coding RNAs that typically inhibit the translation and stability of messenger RNAs, controlling genes involved in cellular processes such as inflammation, cell cycle regulation, stress response, differentiation, apoptosis, and migration. Not surprisingly, microRNAs are also aberrantly expressed in cancer and promote tumorigenesis by disrupting these vital cellular functions. In this review, we first broadly summarize the role of microRNAs in breast cancer and Estrogen Receptor alpha signaling. Then we focus on what is currently known about the role of microRNAs in anti-hormonal therapy or resistance to endocrine agents. Specifically, we will discuss key miRNAs involved in tamoxifen (miR-221/222, 181, 101, 519a, 301, 375, 342, 451, and the let-7 family), fulvestrant (miR-221/222, miR-200 family), and aromatase inhibitor (miR-128 and the let-7 family) resistance.