A 63-year-old female was admitted to our hospital for investigation of serum elevation of carcinoembryonic antigen (CEA). She underwent high anterior resection for a rectal cancer 5-years ago. Chest computed tomography (CT) obtained 5-years ago showed a nodule in the right S10, measuring 1.3 x 0.8 cm in size. The nodule was assessed as benign. Chest CT on admission showed the enlarged nodule with a pleural indentation, measuring 2.2 x 1.6 cm in size. Definitive diagnosis could not be established. Since it was difficult to exclude the possibility of malignancy, video-assisted partial resection was performed. Histological examination of the nodule revealed primary adenocarcinoma in frozen sections. Lobectomy with lymph node dissection was performed. The ultimate diagnosis was adenocarcinoma with mixed subtypes. The tumor was classified as stage IA with T1bN0M0. We reported this case because it was a rare slow-growing adenocarcinoma that had a 5-years clinical history before operation.