CLDN18 and gastric cancer: Another study to analyze the expression, genetic alterations, and prognostic role of CLDN18 using public data from The Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO), and Human Protein Atlas (HPA) databases demonstrated that the expression of CLDN18 was restricted to the lung and stomach in normal tissues and was significantly downregulated in GC but was ectopically overexpressed in some other cancer types.