[Thymic Hyperplasia with Carcinoembryonic Antigen Elevation;Report of a Case].

A 64-year-old man was found to have serum carcinoembryonic antigen(CEA) elevation while undergoing an examination for recurrent gastroenteritis. His past medical history included gastroenteritis, rheumatoid arthritis, and diabetes. Blood testing revealed an increased CEA level of 153.00 ng/ml( normal ≤ 5.00 ng/ml). Chest computed tomography scan revealed an abnormal soft tissue shadow measuring 5.7 × 1.2 × 7 cm in the anterior mediastinum. The soft tissue shadow in the anterior mediastinum was the only abnormality found by whole-body examination. The possibility of a malignant tumor could not be ruled out, and the surgery was performed. Histopathological examination of the specimen confirmed thymic hyperplasia, and immunohistochemical staining detected CEA-positive cells. Serum CEA level normalized at three months after surgery and also 2 years postoperatively.