More recently, immunotherapeutic antibodies that block immune checkpoint molecules have led to the regulatory approval of the anti-cytotoxic T lymphocyte antigen-4 (CTLA-4) antibody ipilimumab for the treatment of metastatic melanoma,24,25 followed by the anti-programmed cell death protein 1 (PD1) receptor antibodies nivolumab and pembrolizumab.26 The gene discussed is PDCD1; the disease is metastatic melanoma.