The diverse roles of circular RNAs in cholangiocarcinoma.

Cholangiocarcinoma (CCA) is a malignant tumor that develops in the extrahepatic bile duct, that is, from the left and right hepatic ducts to the lower end of the common bile duct. Because of its indeterminate etiology, difficulties in the diagnosis of early lesions, easy invasion and metastasis and resistance to chemotherapeutic drugs, the trend of mortality rate deterioration of patients with CCA has not been fundamentally reversed. And the molecular mechanisms underlying the development of CCA are not well characterized. Circular RNA (CircRNA) is an endogenous non-coding RNA with a circular structure. Recent studies have found circRNA involved in multiple physiological processes and participated in the proliferation, invasion, metastasis, immunomodulation, angiogenesis, biometabolism, and chemoresistance of many malignancies, including CCA, pancreatic cancer, liver cancer, and gastric cancer. In this review, we summarize what has been published so far to be related to the biogenesis, functions, and characteristics of circRNAs in CCA and the potential clinical prospects.