CLDN18/claudin 18 is a member of the claudin family of integral membrane proteins that comprise tight junction strands. These are formed at points of cell-cell adhesion at the plasma membrane in epithelial cells. There are two splice variants, one expressed in the gastric mucosa and the other in lung. The gastric isoform is expressed in gastric tumors as well as tumors of other tissues, including the lung, ovary, pancreas, and esophagus. Staining is used to identify gastrointestinal and pancreatobiliary neoplasms such as gastrointestinal signet ring cell carcinoma, pancreatic ductal adenocarcinomas, and intrahepatic cholangiocarcinoma. References: Mol Cell Biol. 2001;21(21):7380-7390. doi: 10.1128/MCB.21.21.7380-7390.2001; Clin Cancer Res. 2008;14(23):7624-7634. doi: 10.1158/1078-0432.CCR-08-1547; Gene. 2011;481(2):83-92. doi: 10.1016/j.gene.2011.04.007; Am J Surg Pathol. 2008;32(8):1182-1189. doi: 10.1097/PAS.0b013e318163a8f8; J Histochem Cytochem. 2011;59(10):942-952. doi: 10.1369/0022155411420569; Virchows Arch. 2011;459(1):73-80. doi: 10.1007/s00428-011-1092-z.