Predictive biomarkers of response to PD-1/PD-L1 immune checkpoint inhibitors in non–small cell lung cancer

Inhibitors of the programmed cell death 1 (PD-1) pathway show the potential to substantially increase the efficacy of therapy for various malignancies, including non–small cell lung cancer (NSCLC). At the same time, substantial effort has been invested in finding biomarkers predicting which patients will respond best to this immune checkpoint inhibition. PD-L1 expression in tumor cells and the tumor microenvironment, genetic alterations and mutational load in tumor cells, and pre-existing immunity and its enhancement during treatment through tumor-infiltrating immune cells have been associated with outcomes of immune checkpoint inhibition. Here, we review the reported predictive biomarkers of response to PD-1 pathway immune checkpoint inhibitors in NSCLC, mainly focusing on results obtained with clinical trials.