Detection of the SYT-SSX fusion transcripts in formaldehyde-fixed, paraffin-embedded tissue: a reverse transcription polymerase chain reaction amplification assay useful in the diagnosis of synovial sarcoma.

Identification of the t(X;18)(p11.2;q11.2) translocation and detection of the resulting SYT-SSX1 or SYT-SSX2 fusion transcripts are useful diagnostic markers for synovial sarcoma. In this study, we developed a polymerase chain reaction (PCR) assay to amplify SYT-SSX fusion transcripts. The primer sequences were designed to generate small PCR products and to amplify sequences of all known SSX genes as fusion partners for the SYT gene. RNA was obtained from formaldehyde-fixed and paraffin-embedded tissues of 22 immunohistochemically characterized synovial sarcomas, 6 of them cytogenetically confirmed as t(X;18) positive. The SYT-SSX fusion transcripts were detected in 21 of the 22 analyzed cases. The type of the fusion was identified by the specific restriction enzyme digestion pattern as SYT-SSX1 in 13 cases and SYT-SSX2 in 7 cases; in 1 case, the type could not be assigned. None of the cases showed involvement of the SSX3, SSX4, or SSX5 genes, the other members of the SSX gene family. In seven cases, the SYT-SSX1 or SYT-SSX2 fusion transcripts were demonstrated in frozen tissue using a different PCR assay. The PCR products were confirmed as SYT-SSX sequences by sequencing in five randomly selected cases. Fifteen other sarcomas and related tumors were negative for SYT-SSX fusion transcripts. The PCR assay used in this study performs well in formaldehyde-fixed and paraffin-embedded tissue, and it shows a high specificity. This assay can be used as an adjunct test for diagnostically difficult cases or in retrospective studies to refine the diagnosis of synovial sarcoma in archival material.