<h4>Background</h4>Immune checkpoint inhibitors (ICIs) have significantly improved survival in patients with advanced non-small cell lung cancer (NSCLC), but may rarely trigger severe immune-related adverse events (irAEs).<h4>Case summary</h4>A 64-year-oldpatient with metastatic squamous NSCLC and high programmed death-ligand 1 (PD-L1) expression developed subacute neurological decline following pembrolizumab therapy, concurrent with rapid progression. This evidence concerns the gene CD274 and non-small cell lung carcinoma.