The treatment of patients with good performance status and advanced stage non–small cell lung cancer has been based on the use of first-line platinum-based doublet and second-line docetaxel. Immunotherapy represents a new therapeutic approach with the potential for prolonged benefit. Although the vaccines studied have not shown benefit in patients with non–small cell lung cancer, immune checkpoint inhibitors against the PD-1/PD-L1 axis showed increased overall survival compared with docetaxel in randomized clinical trials, which led to the approval of nivolumab and pembrolizumab. Because only a minority of patients benefit from this class of drugs, there has been an intense search for biomarkers.