PDCD1 and neoplasm: Immune checkpoint inhibitors (ICIs) act by blocking immune tolerance pathways such as programmed cell death protein 1 (PD-1), programmed death-ligand 1 (PD-L1), or cytotoxic T-lymphocyte antigen 4 (CTLA 4) and helping the immune system to recognize and attack tumor cells; however, cross-reactivity with self-proteins may cause immune-related adverse events (irAEs).