In gastrointestinal cancer, membrane-bound CLDN7 and CLDN18 were proven to offer reliable immunohistochemical markers for the diagnosis of pancreatic ductal neoplasia [164], and CLDN18 has high sensitivity and specificity for diagnosing biliary tract adenocarcinoma or intraepithelial neoplasia [165]. The gene discussed is CLDN18; the disease is intraepithelial neoplasia.