Molecular mechanism of cholangiocarcinoma carcinogenesis

Cholangiocarcinoma (CCA) is a highly malignant cancer of the biliary tract with a poor prognosis, which often arises from conditions causing long‐term inflammation, injury, and reparative biliary epithelial cell proliferation. Several conditions are known to be major risk factors for cancer in the biliary tract or gallbladder, including primary sclerosing cholangitis, liver fluke infection, pancreaticobiliary maljunction, and chemical exposure in proof‐printing workers. Abnormalities in various signaling cascades, molecules, and genetic mutations are involved in the pathogenesis of CCA. CCA is characterized by a series of highly recurrent mutations in genes, including KRAS, BRF, TP53, Smad, and p16^INK4a. Cytokines that are affected by inflammatory environmental conditions, such as interleukin‐6 (IL‐6), transforming growth factor‐β (TGF‐β), tumor necrosis factor‐α (TNF‐α), and platelet‐derived growth factor (PDGF), play an important role in cancer pathogenesis. Prominent signaling pathways important in carcinogenesis include TGF‐β/Smad, IL‐6/STAT‐3, PI3K/AKT, Wnt, RAF/MEK/MAPK, and Notch. Additionally, some microRNAs regulate targets in critical pathways of CCA development and progression. This review article provides the understanding of the genetic and epigenetic mechanism(s) of carcinogenesis in CCA, which leads to the development of new therapeutic targets for the prevention and treatment of this devastating cancer.