Circular RNAs as potential biomarkers for cancer diagnosis and therapy.

Circular RNAs (circRNAs) are a naturally occurring type of universal and diverse endogenous noncoding RNAs which unlike linear RNAs, have covalently linked ends. They are usually stable, abundant, conserved RNA molecules and often exhibit tissue/developmental-stage specific expression. Functional circRNAs have been identified to act as microRNA sponges and RNA-binding protein (RBP) sequestering agents as well as transcriptional regulators. These multiple functional roles elicit a great potential for circRNAs in biological applications. Emerging evidence shows that circRNAs play important roles in several diseases, particularly in cancer where they act through regulating protein expression of the pivotal genes that are critical for carcinogenesis. The presence of abundant circRNAs in saliva, exosomes and clinical standard blood samples will make them potential diagnostic or predictive biomarkers for diseases, particularly for cancer development, progression and prognosis. Here, we review the current literature and provide evidence for the impact of circRNAs in cancers and their potential significance in cancer prognosis and clinical treatment.