Exosomes as Extracellular Mediators of Cancer

We gained new insight into the potential for some types of extracellular RNA called microRNA (miRNA) to influence cancer progression (Cancer Cell 2014). The research suggests that cancer cell exosomes, vesicles that are secreted by cells and present in many biological fluids, and the associated mature miRNA they carry are involved in tumor formation. Since only cancer exosomes contain certain proteins, these could serve as important diagnostic markers that may be more useful in detection of cancers compared to some current diagnostic approaches such as imaging. This important distinction may also give insight into the design of novel cancer therapeutics. exosomesThough the functional roles of miRNAs remain largely unknown, researchers are beginning to understand their importance in influencing transcription and tumor progression in target cells. In this study, we found that breast cancer cells secrete exosomes packed with the necessary proteins to process miRNAs into their mature form, while exosomes from normal non-cancerous cells lacked this ability. We also showed that when cancer exosomes were combined with normal human breast cells and injected into the mammary tissue of mice, the injected cells became cancerous and formed tumors. Conversely, exosomes from sera of healthy donors had no tumorigenic effect. This research suggests a new cell-independent mechanism by which secreted exosomes from cancerous cells are able to process miRNA that can influence and signal non-cancerous cells to become cancerous, demonstrating that RNA released from one part of the body may have the potential to influence cells in distant parts of the body.