The ultrastructure of epithelioid sarcoma.

We have described clinical, histological immunohistochemical and ultrastructural features of four typical examples of epithelioid sarcoma. Smooth-muscle-type focal densities amid fine actin-like filaments in typical epithelioid cells often containing prominent rER have been observed, as well as a structure in the form of a densely granular cytoplasmic body. These features are suggestive of myofibroblastic differentiation. A tumour with light microscopy features typical of epithelioid sarcoma but of spindle-cell appearance is also described. Ultrastructurally this consists of myofibroblasts and it is suggested that this may be an unusual variant in which myofibroblastic differentiation is a major feature.