An 84-year-old woman presented with two large tumors on her chest and back, which had been operated twice. The tumor at the first operation was mainly composed of loosely arranged spindle cells with little atypicality and necrosis, mostly in myxomatous ground substance. At the later stage, the tumor cells showed obvious atypicality, including multinucleated giant cells, and were partly arranged in a storiform pattern. Mitotic figures were rarelly observed. Our tentative diagnosis was malignant peripheral nerve sheath tumor. However, neither S-100 protein nor NSE was positive throughout the course. Therefore, we finally diagnosed her condition as myxoid variant of malignant fibrous histiocytoma. She died of local recurrence and distant metastasis to muscle, lung and liver. [Skin Cancer (Japan) 2000; 15: 39-43]
