The best-characterized ICIs are antibodies that target programmed cell death protein-1 (PD-1) (nivolumab and pembrolizumab), PD-L1 (atezolizumab) and cytotoxic T-lymphocyte antigen-4 (CTLA-4) (ipilimumab), the goal of which is to enhance the immune system for the detection and eradication of tumor cells. Here, PDCD1 is linked to neoplasm.