PDCD1 and cancer: Drugs interrupting immune checkpoints, such as anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), anti-programmed cell death protein 1 (PD-1), anti-programmed cell death-ligand 1 (PD-L1), and others, can enhance anti-tumor immunity and mediate durable cancer regressions 10, 11.