Immune checkpoint inhibitors (ICIs) are approved for use in the treatment of multiple types of cancer and have demonstrated efficacy over previous cytotoxic chemotherapies in clinical trials.1-7 Some of the representative agents are anti-programmed cell death protein 1 (PD-1) antibodies such as nivolumab and pembrolizumab, which are used in non-small cell lung cancer (NSCLC), malignant melanoma (MM), renal cell carcinoma (RCC), and gastric cancer (GC). Here, PDCD1 is linked to cancer.