In phase III clinical trials, anti-PD pathway therapies have produced substantial clinical responses in a subset of patients with variety of cancers [9–12, 54–56], culminating in FDA approval of two immune checkpoint inhibitors, pembrolizumab and nivolumab, both anti-PD-1 monoclonal antibodies, in the treatment of unresectable or metastatic melanoma (pembrolizumab and nivolumab) and NSCLC (nivolumab) [57, 58]. The gene discussed is PDCD1; the disease is cancer.