A 70-year-old woman diagnosed with advanced, non-resectable programmed cell death ligand 1-positive-non-small-cell lung carcinoma was treated with pembrolizumab as first-line therapy. Soon after therapy initiation, she presented with severe dyspnea, and chest computed tomography revealed a soft tissue mass in the lower trachea of the right main bronchus. During bronchoscopy, she became severely hypoxic, and we performed endoscopic tumor ablation and Dumon Y-stent placement. We considered this severe deterioration caused by pseudoprogression, and suggest that it is necessary to perform bronchoscopy and to prepare for the bronchial intervention when treating patients with immune checkpoint inhibitors.