As a new type of non-coding RNA, circRNA is expressed endogenously as a covalently closed, single-stranded circular molecule. According to its origin, circRNA falls into three categories, Exonic circRNA (ecRNA), Intronic circRNA (ciRNA), and Exon-intron circRNA (ElciRNA). circRNA is abundant and conserved across species and also exhibits tissue-specific and cell-specific properties. Importantly, circRNA is stably expressed in saliva, blood, and exosome, which makes it promising biomarker for diagnosis, prognosis and therapeutic response for cancer patients. Furthermore, several studies have indicated that circRNA exhibited a powerful potential in regulating proliferation, apoptosis, angiogenesis, and metastasis, suggesting that circRNA may be an important target molecule in cancer. Therefore, the discovery of disease-related circRNA may provide a new perspective for the diagnosis and treatment of cancer.
