CTLA4 and gastric cancer: Meanwhile, it has been reported that the tumor microenvironment of HER2‐positive gastric cancer has low expression of cytotoxic T‐lymphocyte antigen 4 (CTLA‐4), lymphocyte activation gene 3 (LAG‐3), T‐cell immunoreceptor with immunoglobulin and ITIM domains (TIGIT), PD‐1 and PD‐L1.42