PDCD1 and cancer: Lung cancer is the leading cause of cancer-related mortality worldwide.1 Immune checkpoint inhibitors (ICIs), which target programmed cell death protein 1 (PD-1) and its ligand (PD-L1) or cytotoxic T lymphocyte antigen-4 (CTLA-4) can elicit durable antitumor responses in multiple cancer types, including non-small-cell lung cancer (NSCLC).2–5 Yet, only a minority of patients with advanced NSCLC derive clinical benefit from this treatment.6 Therefore, there is an urgent need to investigate the predictive biomarkers for ICIs treatment effectiveness.