PDCD1 and cancer: To date, there are six drugs approved by the US FDA, for the immunotherapy treatment of different types of advanced cancer, three PD-1 blockers (pembrolizumab, nivolumab and cemiplimab), its PD-L1 ligand (atezolizumab, avelumab and durvalumab) and a CTLA-4 targeting drug (ipilimumab), but many others are still under study [54,55,56].