Immune checkpoint inhibitors, the most common type of cancer immunotherapy, have been successfully used to treat various cancers, including urothelial carcinoma.[11] PD-1, expressed on the surface of multiple immune cells, binds to its ligand, PD-L1, which is expressed by tumor cells and results in the formation of an inhibitory tumor immune microenvironment that facilitates tumor progression. The gene discussed is PDCD1; the disease is cancer.