Detection of SYT-SSX fusion transcripts in paraffin-embedded tissues of synovial sarcoma by reverse transcription-polymerase chain reaction

Objective To assess the feasibility of detecting SYT-SSX fusion transcripts in paraffin-embedded tissues of synovial sarcoma by reverse transcription-polymerase chain reaction (RT-PCR). Methods RT-PCR was used to amplify the SYT-SSX fusion transcripts using archival formalin-fixed paraffin-embedded tumor specimens from a series of 37 synovial sarcoma cases. To investigate the specificity of the SYT-SSX fusion transcripts, a variety of non-synovial sarcoma tumors were included in the study as negative controls. The detected messages derived from fusion genes were confirmed by subsequent sequence analysis. Results SYT-SSX fusion transcripts were detected in 33 of 37 (89.2%) synovial sarcomas. None of the 34 cases of non-synovial sarcoma tumors showed amplified products of SYT-SSX fusion transcripts, although PBGD mRNA was detected in all specimens. Among 33 SYT-SSX-positive synovial sarcomas, 22 tumors had an SYT-SSX1 fusion transcript, whereas 6 tumors had an SYT-SSX2 fusion transcript. Fusion types can not be distinguished in the remaining 5 cases. There was a significant relationship between SYT-SSX fusion type and histologic subtype. All 10 biphasic synovial sarcomas had the SYT-SSX1 fusion, whereas all tumors with SYT-SSX2 were of monophasic morphology (P < 0.05). Conclusions RT-PCR can be applied to archival formalin-fixed paraffin-embedded tumor tissues as a sensitive and reliable technique for the diagnosis and differential diagnosis of synovial sarcoma. There is an association between SYT-SSX fusion type and histological subtype. SYT-SSX2 fusion transcripts can only be found in monophasic synovial sarcoma.