MUC1 and cholangiocarcinoma: Beyond the respiratory tract, MUC4 has been reported to be a novel prognostic factor in patients with invasive ductal carcinoma of the pancreas and chronic pancreatitis [147, 148], intra-hepatic cholangiocarcinoma-mass forming type [149], extra-hepatic bile duct [150] and lung adenocarcinoma [151] and, unlike MUC1, is not associated with metastasis in cholangiocarcinoma [152].