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.