With the United States Food and Drug Administration (US FDA) approval of pembrolizumab, an anti-programmed cell death protein 1 antibody (anti-PD-1) for advanced-stage melanomas [3], the importance of immune-related markers, and especially immune checkpoints (namely PD-1, programmed death-ligand 1 [PD-L1], and lymphocyte activation gene-3 [LAG-3, also known as CD233]) became more prominent. The gene discussed is PDCD1; the disease is melanoma.