A 74-year-old man was found a left completely atelectasis on chest X-ray. He had undergone left lower lobe resection because of an adenocarcinoma at the age of 58. Bronchoscopy revealed a tumor near the left upper lobe branch entry that obstructed the lumen, and a biopsy confirmed the diagnosis of adenocarcinoma. A left completion pneumonectomy was performed, but #4L and #10 lymph nodes could not be completely resected. Programmed cell death 1-ligand 1( PD-L1) was positive with tumor proportion score (TPS) 15%, so chemotherapy with pembrolizumab+pemetrexed+carboplatin was started about 1.5 months after surgery. Pancytopenia appeared from the seventh course and did not improve after discontinuation of chemotherapy, so we consulted to the hematologist. He was diagnosed as aplastic anemia by bone marrow biopsy. Aplastic anemia was unresponsive to treatment and chemotherapy could not be resumed. He died of exacerbation of lung cancer.