Increased carbohydrate antigen 19-9 expression in a thymic neuroendocrine tumor

Here, we report a case of carbohydrate antigen (CA) 19-9-producing mediastinal neuroendocrine tumor (NET) (atypical carcinoid). A 54-year-old woman with no specific relevant medical history was referred to our hospital because of increased CA19-9 (95.3 U/ml) detected on health screening. Chest computed tomography (CT) revealed an anterior mediastinal mass without localized lymphadenopathy. Thoracic surgery was performed and the histopathological diagnosis was thymic CA19-9-positive NET. The patient developed mediastinal lymph node metastasis at 1 year (CA19-9: 413 U/ml) and multiple bone metastases 4 years (CA19-9: 2303 U/ml) after surgery. Increased CA19-9 levels paralleled the clinical courses of relapse. To our knowledge, this is the first report of CA19-9-producing thymic NET.