Erythrocytosis caused by erythropoietin-producing thymic carcinoma.

We describe the first reported case, in an 82-year-old man, of erythrocytosis caused by an erythropoietin (EPO)-producing thymic carcinoma. The patient underwent computed tomography-guided fine-needle aspiration of a 6-cm anterior mediastinal mass, and histological findings revealed thymic squamous cell carcinoma. The existence of EPO was confirmed immunohistochemically using the tumor tissue. Postoperative clinical improvement of erythrocytosis and the decline of EPO suggest a paraneoplastic nature of erythrocytosis as seen in this patient.