Epithelioid sarcoma: a tumour of myofibroblasts.

A case of epithelioid sarcoma of scalp has been studied by light and electron microscopy, histochemistry and immunocytochemistry. The results suggest that epithelioid sarcoma is a tumour of myofibroblasts. The epithelioid appearance results from gross and disordered accumulation of cytoplasmic intermediate filaments (10 nm diameter), possibly of desmin type, producing the misleading light microscopical resemblance to epithelioid histiocytes and biphasic pattern of synovial sarcoma. The cause of the filament accumulation is unknown but it may represent a degenerative change leading to necrosis, a characteristic feature of epithelioid sarcoma.