The patient was a 50-year-old man with a 32 pack-year smoking history. Chest X-ray of the medical check-up showed a mass shadow in the left upper lung field (Figure 1A) without any pain in the chest and back, and the patient was referred to our hospital. Laboratory examinations revealed remarkable elevation of the serum level of carcinoembryonic antigen (CEA; 1253.2 ng/ml). Chest computed tomography (CT) revealed a huge mass shadow of 132 mm in size (Figure 1B), in the left upper lobe with invasion into the lower lobe and main pulmonary artery. The hilar and mediastinal lymph nodes were also swollen. Positron emission tomography/CT revealed a high uptake in the mass, with a maximum standardized uptake value of 19.85 (Figure 1C). The patient underwent transbronchial biopsy and was diagnosed with NSCLC (cT4N2M0, cStage IIIB; Figure 2A). No genetic alterations were identified in epidermal growth factor receptor, anaplastic lymphoma kinase or c-ROS oncogene 1. Two percent of the tumor cells exhibited the expression of programmed death-ligand 1 (PD-L1; 22C3; Figure 2B). Then, carboplatin + nab-paclitaxel + pembrolizumab were administered. During the second cycle, an adverse event (neutropenia: grade three) occurred and the patient could not receive nab-paclitaxel on day 15. After the second cycle, the patient’s serum level of CEA decreased to 202.6 ng/ml. After the administration of pembrolizumab in the third cycle, an immune-related adverse event (infusion reaction: grade 2) occurred and we judged that drug therapy could not be continued. After the third cycle, laboratory examinations revealed that the patient’s serum level of CEA had decreased to 20.8 ng/ml. CT revealed that the mass shadow was reduced to 104 mm in size (-21%: stable disease) and three-dimensional CT showed a remarkable decrease in tumor volume from 448859 mm3 to 85081 mm3 (-81%). No distant metastasis was present. The patient’s good physical capacity, including his pulmonary function, suggested that he could undergo left pneumonectomy. Left pneumonectomy combined with resection of the parietal pleura due to adhesion between the left upper lung and parietal pleura was performed (Figure 2C). The hilar and mediastinal lymph nodes were also dissected. The postoperative course was uneventful with no postoperative complications. The tumorous lesion in the left upper lung exhibited massive necrosis, fibrosis with hyalinization and inflammation. Viable neoplastic cells were observed in less than one percent of the total tumorous lesion, suggesting a near pathological complete response (pCR; Figure 2D, arrow). In addition, no viable cells were identified in the dissected lymph nodes. After surgery, a laboratory examination revealed a further decrease in CEA (1.3 ng/ml; Figure 3). Because of the occurrence of an infusion reaction, we decided to follow-up without postoperative therapy.