PDCD1 and gastric cancer: Recently, immunotherapy, especially immune checkpoint blockade (ICB, e.g. anti-PD1/PD-L1 antibodies), has been used to treat multiple cancers, including NSCLC, melanoma, renal cell cancer, colorectal cancer, recurrent head and neck cancer (squamous cell), urothelial carcinoma, gastric cancer cervical cancer [56].