PDCD1 and cancer: In the last decade, immune checkpoint inhibitors (ICIs), targeting cytotoxic T lymphocyte-antigen-4 (CTLA-4), programmed cell death protein 1 (PD1), and its ligand 1 (PD-L1), have greatly improved the survival of lung cancer and malignant melanoma [1, 2], and their use has expanded in other types of cancer [3].