PDCD1 and cancer: Immune checkpoint inhibitors (ICIs), particularly antibodies targeting programmed cell death 1 (PD-1), programmed death ligand 1 (PD-L1), and anti-cytotoxic T-lymphocyte antigen 4 (CTLA-4), have revolutionized the field of Immuno-oncology and emerged as the standard of care for first- or second-line treatment of a range of cancer types (1, 2).