Pembrolizumab is a humanized monoclonal antibody designed to directly block the interaction between programmed cell death protein 1 (PD-1) and its ligands, leading to T-cell stimulation and anti-tumor response, and it has been successfully used in the treatment of melanoma, lung cancer, renal cancer, and hematological malignancies [1]. The gene discussed is PDCD1; the disease is melanoma.