The program cell death-1/programmed death-ligand 1 (PD-1/PD-L1) pathway plays a critical role in the tumor immune response; thus, anti-PD-1 antibodies (Abs), such as nivolumab and pembrolizumab, are widely used in the treatment of various cancers including advanced melanoma [1–3]. The gene discussed is PDCD1; the disease is neoplasm.