Circulating Exosomes as Biomarkers of Breast Cancer
The proportion of clinically relevant exosomes (CREs) in circulating blood can enable staging of cancer as well as non-invasive monitoring of interindividual variations in tumor-receptor expression levels. One approach to quantification of CREs utilizes a Surface Plasmon Resonance (SPR) platform to determine the proportion of CREs in a two-step strategy that involves; (i) initial isolation of bulk exosome population using tetraspanin biomarkers (i.e., CD9, CD63); and (ii) subsequent detection of CREs within the captured bulk exosomes using tumor-specific biomarkers such as HER2 (Sina et al. 2016). The authors demonstrated isolation of bulk exosome population and detection of as low as 10% HER2-positive exosomes from samples containing designated proportions of HER2-positive BT474 and HER2-negative MDA-MB-231 cell-derived exosomes. Exosomes were successful isolated from a small cohort of breast cancer patient samples with identification of ~14-35% of their bulk population expressing HER2.