PD-1 and PD-L1 Inhibitors in Advanced Non-small Cell Lung Cancer—Promising Agents and Evolving Questions

There exists increasing evidence that PD-1 and PD-L1 inhibitors may be effective in the treatment of non-small cell lung cancer (NSCLC)— an unforeseen finding given the early failure of several immuno- and vaccine-based therapies in this field. This suggests that NSCLC is a more immunogenic tumor than initially appreciated and that it may manipulate various immune checkpoints in order to blunt a potential anti-tumor immune response. NSCLC has subsequently been shown to commonly overexpress PD-L1 as a means of suppressing such cell-mediated immune response through PD-1-mediated signaling. Numerous PD-1 and PD-L1 inhibitors are currently in development as well as various combinations of these inhibitors with chemotherapy, kinase inhibitors, and other immune checkpoint inhibitors. Although these treatments have demonstrated clinical activity in early phase clinical trials, reliable data on the impact of these agents on clinically meaningful endpoints in advanced NSCLC remains scarce. Important questions remain unanswered regarding the appropriate use of PD-L1 expression as a predictive biomarker for the use of these agents as well as the ability of the aforementioned drug combinations to achieve durable disease control.