PDCD1 and cancer: Checkpoint inhibitors (CPIs), including anti-programmed cell death protein 1/programmed death-ligand 1 (PD1/PD-L1) and anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) monoclonal antibodies, are now widely used across multiple cancer subtypes in the setting of metastatic, adjuvant and neoadjuvant indications [1].