Exosome-encapsulated microRNAs as circulating biomarkers for breast cancer

Breast cancer is a highly prevalent disease, accounting for 29% of invasive cancers in women. Survival from this disease depends on the stage at diagnosis, with patients who are detected earlier having more favourable outcomes. It is because of this that research groups are focusing on the development of a blood-based biomarker for breast cancer. Such biomarkers may facilitate the detection of breast cancer in its infancy before it has spread beyond the primary site. MicroRNAs (miRNAs) have shown immense potential in this setting. These short, non-coding RNA sequences have been shown to be dysregulated in breast cancer. Despite showing immense promise, miRNAs have not been successfully implemented in the clinical setting due to a lack of a standardised approach which has resulted in conflicting results. These challenges may be addressed at least in part through the study of exosomes. The biomarker potential for exosomes holds huge promise and may revolutionise the way in which we diagnose and manage breast cancer. These nanovesicles may be isolated from a variety of bodily fluids, including serum, and their miRNA content has been shown to reflect that of the parent breast cancer cell. This review will highlight the nomenclature and defining characteristics of exosomes, and current methods of isolation of serum-derived exosomes. Initial promising reports on the potential utility of exosomal miRNAs to be used as breast cancer biomarkers will also be addressed.