Therapeutic blockade of the PD-1/PD-L1 interaction by immune checkpoint inhibitors (ICI) has transformed the management of advanced melanoma; with objective responses in 35-40% of patients (8, 9), with 35% progression-free at 1-year (10, 11), and 34% alive at 5-years (12). The gene discussed is PDCD1; the disease is melanoma.