Further comparison between tumor samples and normal samples revealed significant differences in CRC, STAD, LUAD, LUSC, ESCA, and kidney renal papillary cell carcinoma (KIRP), and the CLDN18 expression levels in the remaining four cancers were significantly higher in normal samples than in tumor samples, except for CRC and KIRP (Figure 2B). The gene discussed is CLDN18; the disease is cancer.