Immune Checkpoint Inhibitors in Lung Cancer: Imaging Considerations

OBJECTIVE: The purpose of this article is to review the mechanisms of action of immune checkpoint inhibitors in the treatment of non-small cell lung cancer (NSCLC), highlight imaging manifestations of common adverse events, and discuss new criteria for using imaging to assess unique treatment response patterns. CONCLUSION: Immune checkpoint inhibitor therapy is a breakthrough in cancer treatment that has shown unprecedented success when used for a variety of malignancies. In recent phase 3 clinical trials for NSCLC, monoclonal antibodies that target the programmed death-1 (PD-1) receptor and its ligand PD-L1 (i.e., the PD-1/PD-L1 axis) were associated with better overall survival in head-to-head comparisons with conventional cytotoxic chemotherapy. On the strength of the results of these trials, the PD-1 inhibitors nivolumab and pembrolizumab and the PD-L1 inhibitor atezolizumab recently received regulatory approval by the U.S. Food and Drug Administration for the treatment of advanced NSCLC. Because of their unique mechanisms of action, these agents differ from conventional cytotoxic chemotherapy in both patterns of treatment response and treatment-related adverse events. Given the rapidly expanding clinical use of immune checkpoint inhibitors and the central role of radiology in the care of patients with lung cancer, it is important for radiologists to be familiar with these agents and their unique imaging findings.