Epithelioid sarcoma: case report with ultrastructural review, histogenetic discussion, and chemotherapeutic data.

A case of abdominal wall epithelioid sarcoma, studied by light and electron microscopy over a 3-year period, is presented. Ultrastructurally, there appear to be two types of tumor cells, light and dark, which differ by virtue of a heavier concentration of microfibrils and dilated rough endoplasmic reticulum in the dark cells. Both tumor cell types contain prominent Golgi systems, abundant free ribosomes, and numerous pinocytotic vesicles. The ultrastructural characteristics of the tumor cells resembel those of epithelioid cells of experimental human granulomas, as well as those of normal human synovium. A multifaceted relationship between histiocytes and synovial cells is demonstrated and it is concluded that the tumor is probably derived from mesenchymal reserve cells capable of differentiating a long histiocytic or synovial lines. Preliminary chemotherapeutic data are reviewed.