Ultrastructural similarities and differences of synovial sarcoma, epithelioid sarcoma, and clear cell sarcoma of the tendons and aponeuroses.

The ultrastructural features of synovial sarcoma, epithelioid sarcoma, and clear cell sarcoma of the tendons and aponeuroses were compared to identify differential markers and similarities. A continuous spectrum of modulation of morphologic features of synovial and epithelioid sarcomas was observed. Biphasic synovial sarcoma with pseudoglandular and stromal components represents one extreme of this spectrum. The gradual disappearance of the pseudoglands and the formation of nests of epithelial-like cells, which are characteristic of epithelioid sarcoma, were observed. The cells of clear cell sarcoma, as well as those of synovial and epithelioid sarcomas, form epithelial-like islands; however, the presence of premelanosomes in the former is a feature of neural crest derivatives.