In the gastric mucosa of gastric cancer patients, the expression level of PD-1/PD-L1 is significantly higher than in the general population [53], and in the gastric mucosa of early-stage gastric cancer patients and high-grade gastric intraepithelial neoplasia infected with H. pylori, the expression level of PD-L1 is also significantly higher than that of patients with low-grade gastric intraepithelial neoplasia [54]. Here, PDCD1 is linked to gastric cancer.