In patients with advanced urothelial carcinoma, promising clinical activity has been shown for antibodies targeting the programmed cell death-1 (PD-1)/PD-ligand 1 (PD-1/PD-L1) checkpoint, but when different algorithms have been used to assess high vs. low/negative PD-L1 expression, the extent of concordance of the available PD-L1 immunohistochemical (IHC) assays has been poorly defined. The gene discussed is PDCD1; the disease is urothelial carcinoma.