Circular RNAs: Promising biomarkers for cancer diagnosis and prognosis.

Circular RNAs (circRNAs), a group of non-coding RNA characterized by the presence of covalent bonds linking 3' and 5' ends, act as miRNA sponges to participate in the tumorigenesis. Being stable, conserved and cell- or tissue-specific, circRNAs have shown their potentials as molecular markers for cancer. Convenient and noninvasive approaches may be developed based on the roles of circRNAs to diagnose or predict the prognosis of tumors. Although most of the potential mechanisms are not entirely clear, circRNAs have shown a universal and critical role in regulating cellular processes of cancers. This review summarized the classification, formation, characteristics, detection, and biological functions of circRNAs. We proposed the possibility of using circRNAs as biomarkers for cancer diagnosis, treatment and prognosis.