Plama MicroRNAs: a Biomarker for Cancer Diagnosis

MicroRNA is a single-stranded RNA, consisting of about 22 nucleotides in length. It has been found that microRNAs play roles in development and cellular processes. It can be classified as oncogenic and tumor suppressor factors. For microRNA expression in cancer, it has been found that the expression levels of oncogenic microRNAs are increased, whereas tumor suppressor microRNAs are decreased. Therefore, microRNAs can possibly be a potential biomarker for cancer diagnosis. In cholangiocarcinoma (CCA), it was shown that miR-21 expression level was significantly increased in CCA tissues when compared to normal bile ducts. Moreover, there are many reports that microRNAs can be secreted from cells and found in blood circulation. In gastric cancer, the concentration of miR-106b was analyzed in plasma. It was found that the concentration of miR-106b was significantly higher in plasma taken from gastric cancer patients than that of healthy controls. Plasma microRNAs are resistant to RNase activity. In prostate cancer, it was found that serum levels of miR-141 could be differentiated patients with metastatic prostate cancer from healthy controls. The measurement of tumor derived microRNAs in serum or plasma may be a new approach for the biomarker in blood-based diagnosis of human cancer.