Currently, the most investigated biomarker as a predictor for anti-PD-1 response is tumor PD-L1 expression, determined by immunohistochemistry (IHC) in tumor tissue in lung, urothelial, and gastric cancers, but its low specificity, 62–72% across trials [24,25,26], is a limitation since approximately 20% of melanoma patients with negative expression also benefit from anti-PD-1 treatment [7,9]. The gene discussed is CD274; the disease is neoplasm.