Claudin 18 (CLDN18) belongs to the large claudin family of proteins,which are tetraspan transmembrane proteins of tight junctions . Claudins exhibit specific patterns of expression in different tissues . CLDN18 is specifically expressed in the stomach and lung. CLDN18 has two alternatively spliced variants,CLDN18.1 and CLDN18.2. CLDN18.2 is a highly selective gastric lineage marker that determines the gastric phenotype in a neoplastic condition,whereas CLDN18.1 is lung specific . Altered CLDN18 expression has been reported in various human malignancies,including gastric cancer,lung adenocarcinoma,and pancreatic neoplasm .