Cholangiocarcinoma arises from malignant transformation of cholangiocytes lining the intra- or extrahepatic bile ducts. Chronic inflammation from conditions such as primary sclerosing cholangitis (PSC), liver fluke infection, or hepatolithiasis drives repeated cycles of epithelial injury and repair, promoting oncogenic mutations (TP53, KRAS, IDH1/2). The tumor causes progressive biliary obstruction, leading to conjugated hyperbilirubinemia, cholestasis, and eventual hepatic dysfunction. Perihilar (Klatskin) tumors are the most common subtype.