Clear-cell sarcoma of tendons and aponeuroses. An immunohistochemical and electron microscopic analysis indicating neural crest origin.

A clinico-pathological, light microscopic and immunohistochemical study of 15 clear-cell sarcomas, with an ultrastructural analysis of 6 of the tumors, is presented. The tumors showed a strong predilection for tendons and aponeuroses of the extremities in predominantly young and middle-aged people. The clinical setting, course and light microscopic appearance agree well with the original description by Enzinger (1965). Nine of the 15 patients developed metastases, most of them including lymph nodes, and 8 of the patients had died at the time of follow-up (median follow-up time 4.8 years). Reducing pigment was demonstrated within the cells of 2 tumors. Ultrastructurally the 6 tumors studied had a uniform appearance with characteristically rounded or oval tumor cells with a single nucleus containing one or two very prominent nucleoli, a light-staining cytoplasm with a moderate amount of organelles and a variable content of glycogen. Polymorphic melanosomes were seen in the cells of one of the tumors. External laminas enclosed groups of tumor cells and invested parts of individual tumor cells. With immunoperoxidase analysis for S-100 protein positive staining was observed in the vast majority of the tumor cells of all 15 clear-cell sarcomas. Metastases appearing in 9 of the 15 cases showed positive staining for S-100 protein. There was a strong staining of the cytoplasm and generally a weak and varying staining of nuclei. The immunohistochemical and electron microscopic findings indicate that clear-cell sarcoma is a homogenous entity among soft tissue sarcomas, of probable neural crest derivation.