Circulating circRNAs at the frontier of cancer detection, prognosis, and therapy

Circular RNAs (circRNAs) are distinguished from other noncoding RNAs by their unique loop structure, without 5' polar ends and 3' polyadenylated tails. They are stable and abundant in a wide range of eukaryotic taxa and exert functions via interactions with microRNAs (miRNAs), proteins, and DNA, including tumor-suppressive or oncogenic functions. Emerging evidence suggests that circRNAs show specific expression patterns in tumor tissues or circulation and changes in expression with respect to tumor stage; therefore, they possess strong potential as diagnostic, prognostic, and predictive biomarkers. Nevertheless, translating theoretical achievements in circRNA research to clinical practice is challenging. Herein, this review focuses on the important functions of circRNAs, including their roles in cancer, highlighting their utility for early cancer detection, prognosis, and treatment, in addition to a summary of vital detection methods for circulating circRNAs.