Current evidence seem to support the notion that papillary tumors of the biliary tree share many biological and morphologic similarities with IPMN [174], and are thus not a fundamentally different “species.” Contrary to the common assumption that these tumors arise from biliary epithelium, many cases of bile duct papillary tumors exhibit expression of MUC2, CDX2, and cytokeratin 20 [174], as they can also have pancreaticobiliary, gastric, and intestinal subtypes. The gene discussed is KRT20; the disease is pancreatic intraductal papillary-mucinous neoplasm.