Cancer immunotherapy, notably monoclonal antibody (mAb) antagonists of the programmed cell death protein 1 (PD-1)/programmed cell death-ligand 1 (PD-L1) pathway, has shown significant promise for the treatment of a variety of solid tumor types, including non–small-cell lung cancer (NSCLC) (1) and melanoma (2). The gene discussed is PDCD1; the disease is cancer.