Epithelioid sarcoma with SYT-SSX1 fusion gene expression: molecular and cytogenetic analysis.

Epithelioid sarcoma is a rare malignant soft tissue tumor of unknown histogenesis, characterized by the epithelioid morphology of tumor cells and co-expression of epithelial and mesenchymal lineage proteins. A common epithelial and mesenchymal immunophenotype is also found in another soft tissue tumor, the biphasic subtype of synovial sarcoma. Furthermore, the presence of a breakpoint at 18q11 in epithelioid sarcoma, similar to that found in synovial sarcoma, has been reported. These facts would support the hypothesis that both tumors may share a common histogenetic background. However, expression of the SYT-SSX fusion genes has been investigated in epithelioid sarcoma with negative results. We report, to our knowledge, the first epithelioid sarcoma in which the presence of SYT-SSX1 fusion gene has been detected by means of conventional RT-PCR analysis and sequencing, real-time RT-PCR and FISH. The SYT-SSX1 gene fusion was identified in a small proportion of tumoral cells. This finding supports a likely common histogenetic background for both epithelioid sarcoma and synovial sarcoma.