MicroRNAs have been reported to be stably detectable in plasma/serum and to exhibit resistance to endogenous ribonuclease activity because of binding to proteins such as Argonaute-2 and high-density lipoprotein, or being packed by secretory particles such as exosomes. These secretory particles include specific microRNAs and can function as intercellular transmitters. These findings could open-up a new and promising field in the use of circulating microRNAs for cancer treatment. In particular, miR-18a, which is located in the potentially oncogenic miR-17-92 cluster, is a highly expressed microRNAs in several types of cancers. The concentration of miR-18a in plasma/serum of patients with cancer such as esophageal (AUC=0.944), pancreatic (AUC=0.936), hepatocellular (AUC=0.881), colorectal and other types of cancers is much higher than that of healthy volunteers. Such reports provide evidence that circulating miR-18 might be a next-generation biomarker and contribute to cancer screening in non-invasive liquid biopsy, to a clinically-satisfactory degree of sensitivity and specificity.
Keywords: liquid biopsy; microRNAs; plasma biomarker; review.