Coincidence of Thyroid Transcription Factor-1-Positive Thymoma and Pulmonary Adenocarcinoma

Thyroid transcription factor-1 (TTF-1) has been widely used as a marker of primary lung cancer. However, there have been few reports on TTF-1 expression in thymomas. We here report the case of an asymptomatic 63-year-old man who presented with a right upper lung nodule and cystic mid-mediastinal tumor. The right upper lobe of the lung and the mediastinal tumor were resected. Histological examination of the operative specimen revealed TTF-1-positive type B2 thymoma and invasive pulmonary adenocarcinoma. Although rare, thymoma should be included in the different diagnosis of TTF-1-positive tumors.