Which of the following is the MOST common site of cholangiocarcinoma?

Cholangiocarcinoma is a mucin producing adenocarcinoma arising from the bile ducts. It can be either intrahepatic, hilar or extrahepatic in origin. Most common location of the cancer is hilar (65%) followed by peripheral (30%). Nodular tumors arising at the bifurcation of the common bile duct are called Klatskin tumors and are often associated with a collapsed gallbladder. Predisposing factors for development of cholangiocarcinoma are primary sclerosing cholangitis and liver fluke in Asians, especially Opisthorchis viverrini and Clonorchis sinensis. Patients typically presents as painless jaundice, with pruritus or weight loss. Diagnosis is made by biopsy, percutaneously for peripheral liver lesions, or more commonly endoscopic retrograde cholangiopancreatography (ERCP) under direct vision for central lesions. The tumors often stain positively for cytokeratins 7, 8, and 19 and negatively for cytokeratin 20.