MUC5AC and pancreatic intraductal papillary-mucinous neoplasm: The oncocytic type IPMN also occurs in MD-IPMNs, mostly in the pancreatic head, expresses MUC1+, MUC2-, and MUC5AC+, and exhibits high-grade dysplasia; however, it is exquisitely rare, produces little mucin relative to the other types, and similar to other tumors with increased intra-cytoplasmic mitochondria, appears to have a different biological pathogenesis.