[Metastatic lung tumor developing 15 years after resection of invasive thymoma]

A 57-year-old man with myasthenia gravis had undergone extended thymothymomectomy for invasive thymoma and postoperative irradiation 15 years ago. At present, an abnormal shadow on his left lung field on chest X-ray and an elevated SCC-Ag level led us to suspect primary lung cancer (squamous cell lung cancer). He underwent left lower lobectomy and partial resection of the upper lobe. After the operation, this tumor was identified pathologically as a thymoma. Comparing this tumor with the previous invasive thymoma, we concluded that the present lesion was a metastasis of the former thymoma. This case suggests that a metastatic lung tumor should be suspected when an abnormal shadow is detected on chest X-ray following extended thymothymomectomy for invasive thymoma.