CTLA4 and gastric cancer: Blocking antibody for immune checkpoints such as programmed death-ligand 1 (PD-L1), programmed cell death 1 (PDCD1) and cytotoxtic T-lymphocyte antigen 4 (CTLA4), have been used to treat several tumors including melanoma, renal cell carcinoma, lung cancer and gastric cancer [13, 14].