CLDN18 and pancreatic intraductal papillary-mucinous neoplasm: In gastric cancers, CLDN18 has been shown to be reduced [17], while its upregulation has been reported in pre-neoplastic conditions such as Barrett’s esophagus, mucinous cystic neoplasms, and intraductal papillary mucinous neoplasms [156,157,158].