PDCD1 and cancer: Immune checkpoint inhibitor (ICI)–based immunotherapy, which mainly targets cytotoxic T lymphocyte–associated protein 4 (CTLA-4), programmed cell death 1 (PD-1), and its ligand (PD-L1), has shown remarkable clinical benefits to patients with advanced-stage cancers.1 Early studies2 suggest that ICI response may be associated with PD-L1 protein levels, tumor mutational burden, neoantigens, tumor-infiltrating lymphocytes (TILs), T cell receptor clonality, and transcriptional signatures.