At the moment, immunohistochemistry (IHC) is the standard biomarker used to evaluate PD-L1 expression on tumor cells and not only informs treatment decisions but also regulatory approval, with a threshold at 50% of positive tumor cells for pembrolizumab in first-line treatment for advanced NSCLC, and 1% for pembrolizumab in second-line or durvalumab in consolidation after chemo-radiotherapy in locally advanced NSCLC. The gene discussed is CD274; the disease is neoplasm.