Primary malignant fibrous histiocytoma of skin.

Three fibrous histiocytomas, primary in skin, were studied by light and electron microscopy and by frozen section histochemistry. The term malignant was applied to cutaneous tumors which demonstrated aggressive multinodular local growth, including angioinvasion and/or extension into bone, muscle, and fascia. Metastases were not found. Strongly positive reactions for hydrolytic enzymes, particularly acid phosphatase will help differentiate malignant fibrous histiocytoma from most other primary soft tissue malignancies of skin. Electron microscopic studies reaffirm the presence of both histiocyte-like and fibroblast-like cells. Langerhans' granules were not identified. Primary malignant fibrous histiocytoma of skin may have a prognosis superior to homologous tumors arising in deeper soft tissue and the retroperitoneum.