Epithelioid sarcoma. A light and electron microscopic study suggesting a synovial origin

Two cases of “epithelioid sarcoma” were studied by light and electron microscopy. In both cases, the tumor consisted of a collagen‐rich fibrous stroma with nests of large epithelial‐like cells with acidophilic cytoplasm, giving the neoplastic tissue a biphasic pattern. The ultrastructural study showed that the tumor cells were of three types: “clear” and “dark” cells (recalling those of the synovium and synovial sarcoma) with distorted nuclei and abundant cytoplasm, and a less common, more immature cell. The histologic and ultrastructural features of the neoplastic cells, as well as those of the ground substance, indicate that the tumor is neither of chrondroid nor of histiocytic origin. The cells of the epithelioid islands are similar to the stromal component of synovial sarcoma. It is suggested that epithelioid sarcoma may be a variant of this tumor.