These have been described as cases of pseudoprogression (PP). PD-L1-positive lung malignancy presenting as severe tracheal stenosis, caused by PP after first administration of pembrolizumab, rescued by a Dumon Y-stent. 2.?Case statement A 70-year-old woman visited a regional hospital with a productive cough and lymphadenopathy of her left neck. She experienced a history of smoking 20 smokes daily for the past 40 years. Her TSLPR medical history was unremarkable. Chest radiography revealed a tumor shadow in the right lung apex and multiple bilateral lung nodules. Lung malignancy was suspected, and she was referred to Miyazaki Prefectural Miyazaki Hospital for further examination, where she was diagnosed with NSCLC by core-needle biopsy from her left supraclavicular lymph node. The tumor cells were immunohistochemically positive for CK7 and AE1/AE3 but unfavorable for CK20, thyroid transcription factor 1, and p40. Neuroendocrine markers synaptophysin, chromogranin A, and CD56 were not expressed, and EGFR gene mutations and ALK gene translocations were undetected. The tumor tested 75% positive for PD-L1 expression using the anti-PD-L1 antibody clone 22C3. The chest radiograph showed a nodule in the middle of the right lung, mediastinal lymphadenopathy, and tracheobronchial stenosis. Computed tomography (CT) revealed a solitary 2.0-cm pulmonary mass in the right lower lobe and lymphadenopathy in the mediastinum (Fig. 1). The interval between CT at the former hospital and CT at our hospital was about 2 weeks, but no progression was observed. The TNM stage was cT1bN3M1c (brain, lymph nodes) stage IV [7], and the patient was treated with pembrolizumab as first-line therapy. Open in a separate windows Fig. 1 Chest X-ray and computed tomography (CT) prior to pembrolizumab treatment. (a) Radiograph showing a nodule in the middle of the right lung, mediastinal lymphadenopathy, and tracheobronchial stenosis. Chest CT image shows enlarged mediastinal lymph nodes at (b) trachea level and (c) carina level. Abbreviation: CT, Computed Tomography. Soon after pembrolizumab therapy initiation (day 12), the patient visited our hospital for emergency care, complaining of a productive cough and dyspnea. Her vital indicators were as follows: heat, 36.8?C; blood pressure, 132/83?mmHg; pulse, 107/min; and respiratory rate, 20/min with a reduced O2 saturation of 86% on room air. Her chest exam revealed decreased breath sounds in the right lower lung and diffuse inspiratory and expiratory wheezes. Hemogram results revealed a normal leucocyte count of 11,150/L, and the renal and liver parameters were normal. The LDH and C-reactive protein levels were increased at 387 IU/L and 1.23 mg/dL, respectively. The chest CT revealed a soft tissue mass in the lower trachea to the right main bronchus. (Fig. 2). There were several enlarged mediastinal lymph nodes, but no progression was observed. Bronchoscopy confirmed a soft tissue mass obstructing the lower trachea to such an extent that it impossible to explore the right main bronchus (Fig. 3). We presumed that this patient’s tracheal stenosis was due to tumor invasion of the trachea lumen from your mediastinal lymph node. Because the patient became severely hypoxic by tracheal stenosis during the bronchoscopy, we decided on prompt bronchial intervention. Open in a separate windows Fig. XMD16-5 2 Chest X-ray and XMD16-5 computed tomography (CT) after pembrolizumab administration. (a) Radiograph showing right pleural effusion, mediastinal lymphadenopathy, and tracheobronchial stenosis. Chest CT image shows enlarged mediastinal lymph nodes and a soft tissue mass in the trachea and right main bronchus at (b) trachea level and (c) carina level. Abbreviation: CT, Computed Tomography. Open in a separate windows Fig. 3 Endoscopic view of lower part of the trachea. (a). Trachea is almost occluded by a whitish soft tissue mass obstructing the left main bronchus. (b) Close-range photograph. The patient underwent endoscopic tumor ablation and XMD16-5 stent placement using a Dumon rigid bronchoscope (Efer Medical, La Ciotat Cedex, France) under general anesthesia. At the start of the intervention, disappearance of the endotracheal-endobronchial soft tissue was observed. Endoscopically, rough soft tissue rose from the right tracheal wall, and mucosal erosion with edema was found in the tracheal and right main bronchus. We performed argon plasma coagulation and microwave coagulation therapy for.