The durable clinical benefit of monoclonal antibodies against PDCD1 (PD-1) and CD274 (PD-L1) [together PD-(L)1] in selected patients has revolutionized the care of patients with advanced cancer, with approvals in multiple tumor types and pan tumor indications [microsatellite instability high (MSI-H)/mismatch repair deficient] and tumor mutation burden high [TMB-H; ≥10 mutations/megabase (Muts/Mb)] (1–3). The gene discussed is PDCD1; the disease is neoplasm.