Immune checkpoint inhibitors (CIs), such as anti-CTLA-4 and anti-PD-1 blocking antibodies (Table 1), target the inhibitory receptors on T-cells, including programmed cell death protein-1 (PD-1) and cytotoxic T-lymphocyte-associated protein-4 (CTLA-4), with the goal of enhancing anti-tumor T-cell function. This evidence concerns the gene PDCD1 and neoplasm.