Sarcomatoid Thymic Carcinoma Arising in Metaplastic Thymoma

Metaplastic thymoma is an extremely rare tumor. To date, only 17 cases of metaplastic thymoma have been reported. To the best of the authors’ knowledge, this is the second reported case of a sarcomatoid carcinoma arising in metaplastic thymoma; the carcinoma in this case is larger than that in the previous case. A 63-year-old woman with cough and asthenia for 2 weeks was admitted to the hospital. Computed tomography (CT) revealed a giant mass on the right side of the front mediastinum medium. The mediastinal tumor was excised, and additional pathological examinations, immunohistochemical tests, and electron-microscopic tests were performed. The tumor was diagnosed as a sarcomatoid carcinoma arising in metaplastic thymoma. Here, the authors discuss the clinical pathology of the sarcomatoid carcinoma arising in metaplastic thymoma and describe the biological behaviors with respect to the pathological features.