Anti-PD-1 and anti-PD-L1 (PD-[L]1) monoclonal antibodies, known as checkpoint inhibitors (CPIs), have transformed cancer care, and are approved for use in multiple tumor types and pan tumor indications (microsatellite instability high/mismatch repair deficient [MSI-H/dMMR] and tumor mutation burden [TMB] ≥ 10 mutations/megabase [Muts/Mb])1–3. The gene discussed is PDCD1; the disease is neoplasm.