Pointed Progress in Second-Line Advanced Non–Small-Cell Lung Cancer: The Rapidly Evolving Field of Checkpoint Inhibition

PURPOSE: Non-small-cell lung cancer (NSCLC) is globally prevalent and associated with high rates of mortality. Immune checkpoint pathways are often exploited by tumors to evade immunity-mediated destruction, and checkpoint inhibitors can reactivate tumor-related immune responses. This review considers available clinical evidence for the use of checkpoint inhibitors in the treatment of second-line advanced NSCLC. METHODS: Our systematic search revealed 20 clinical trials evaluating checkpoint inhibitors in the second-line setting, three of which were randomized trials comparing programmed cell death protein 1 and programmed death ligand 1 (PD-L1) inhibitors to docetaxel, the current standard of care in this setting. RESULTS: A randomized phase II trial comparing the PD-L1 inhibitor atezolizumab to docetaxel did not demonstrate improved survival for atezolizumab in patients overall, although a trend toward improved survival with increased PD-L1 expression was apparent. Twin phase III trials showed significantly improved survival for the programmed cell death protein 1 inhibitor nivolumab compared with docetaxel in patients with both squamous and nonsquamous disease. PD-L1 expression correlated with improved survival in patients with nonsquamous disease, and patients with low levels of PD-L1 expression (< 10%) and those with EGFR mutations are unlikely to benefit. Checkpoint inhibitor therapy is generally well tolerated and associated with low rates of grade 3 or 4 adverse events compared with standard care. CONCLUSION: Level 1 evidence exists to support the use of nivolumab as second-line treatment of patients with squamous advanced NSCLC, as well as in select patients with nonsquamous disease. Benefits remain unknown in patients with targetable driver mutations, and use of PD-L1 expression to guide therapy remains controversial. Results from ongoing randomized trials evaluating biomarkers and other checkpoint inhibitors will further our understanding of this rapidly evolving area of oncology.