Mucinous cholangiocarcinoma is the rarest type of cholangiocellular carcinoma,12, 20 and this carcinoma is reported to be derived from IPNB.15, 16, 21 IPNB is pathologically characterized by prominent intraductal papillary proliferation with delicate fibrovascular cores and frequent mucin hypersecretion,15, 16, 21 and it is regarded as the biliary counterpart of intraductal papillary mucinous neoplasm of the pancreas. Here, MUC5AC is linked to carcinoma.