A case of epithelioid sarcoma.

A case of a 58-year-old man with epithelioid sarcoma is reported. Small nodular lesions, up to 10×10 mm in diameter, were present on the scalp, face and upper arm. On chest X-ray examination, the nodular lesions were noticed in the right upper and middle lung field. Biopsy specimen of a scalp nodule and lung lesion showed granulomatous changes composed of irregular-shaped eosinophilic cells with nuclear atypism, spindle-shaped fibroblast-like cells and a few multinucleated giant cells. Electron microscopic examination revealed that two types of cells, dark cells and light cells, were present in the dermal lesion. The cytoplasm of the dark cell contained a large amount of dilated rough-surfaced endoplasmic reticulum and well-developed protocollagen. This finding suggests that the dark cell tends to differentiate towards a fibroblast. Most of light cells had some underdeveloped rough-surfaced endoplasmic reticulum but no filamentous elements. A few exceptional light cells have considerable rough-surfaced endoplasmic reticulum. It therefore seems that the clear cell has a potencial for differentiation towards a histiocyte. These findings suggest that epithelioid sarcoma cells derive from undifferentiated mesenchymal cells.