[A patient with mediastinal liposarcoma showing dedifferentiation].

A 70-year-old man visited our hospital with fever and general malaise. Chest CT scanning showed a large tumor shadow in the anterior mediastinum. The tumor was resected. It consisted of a portion rich in fat on the anterior mediastinal side and a solid portion on the left thoracic cavity side. Pathological examination demonstrated liposarcoma (myxoid type). The solid portion was considered to have resulted from dedifferentiation of the cystic portion. Mediastinal liposarcoma accounts for less than 1% of all mediastinal tumors. To our knowledge, there have been no previous reports of patients with myxoid-type mediastinal liposarcoma showing dedifferentiation.