The correlation analysis between TM4SF18 and checkpoint gene expression showed that TNFRSF9, CD44, CD86, TNFSF15, CD40, TNFRSF4, VSIR, TNFESF8, PDCD1LG2, TNFSF14, CD80, CD276, HAVCR2, CD28, and CD48 in GC were highly correlated in expression (Fig. 8B). The gene discussed is PDCD1LG2; the disease is gastric cancer.