Regulation of cancer metastasis by cell-free miRNAs

• Cell-free miRNAs have been detected in various body fluids of cancer patients.
• Levels of specific miRNAs change in metastatic compared non-metastatic patients.
• These could be used for diagnosis, prognosis and treatment of metastasis.
• The functional role of several cell-free miRNAs in metastasis has been investigated.

MicroRNAs (miRNAs) are integral molecules in the regulation of numerous physiological cellular processes that have emerged as critical players in cancer initiation and metastatic progression, both by promoting and suppressing metastasis. Recently, cell-free miRNAs shed from cancer cells into circulation have been reported in cancer patients, raising hope for development of novel biomarkers that can be routinely measured in easily accessible samples. In fact, establishing miRNA expression in the circulation likely has advantages over determination in primary tumor tissue, further augmenting the potential applications of miRNA detection in oncological practice. In addition, secretion of miRNAs impacting distant cell signaling or promoting the formation of a niche that sustains a distant tumor microenvironment allows for new treatment approaches to thwart cancer progression.