In the TCGA pan-cancer cohort, PAAD, CRC, STAD, and LUAD expressed higher levels of CLDN18, whereas lower grade glioma (LGG), prostate adenocarcinoma (PRAD), glioblastoma multiforme (GBM), and ovarian serous cystadenocarcinoma (OV) had lower levels of CLDN18 expression (Figure 2A). This evidence concerns the gene CLDN18 and central nervous system cancer.