PDCD1 and cutaneous melanoma: ,13 Several studies have made the point that the failure of CPIs blocking programmed cell death 1 (PD1) and cytotoxic T-lymphocyte associated protein 4 (CTLA4) pathways in metastatic UM may be due to the higher importance of additional inhibitory pathways; while prevalence of expression of PD-L1 (the ligand for PD1) is lower in UM than in cutaneous melanoma,14 studies of primary and metastatic UM tumors have found elevated expression of TIGIT, IDO1, TIM3, and LAG3.15