Micromanagers of malignancy: role of microRNAs in regulating metastasis

It has become evident that cancer pathogenesis involves, among other macromolecules, a class of small regulatory RNAs named microRNAs, and that microRNA expression profiles are associated with prognosis and therapeutic outcome in several human cancers. Although the oncogenic or tumor-suppressing functions of several microRNAs have been characterized, the mechanistic roles played by microRNAs specifically in mediating metastasis have been addressed only recently. In this review, we focus on our emerging understanding of the contributions of microRNAs to malignant progression, specifically their functions in mediating tumor invasion and metastasis. These findings illuminate the molecular basis of metastasis and begin to connect small-RNA discoveries to the development of novel clinical biomarkers and therapeutic targets in neoplastic diseases.