Detection of SYT-SSX fusion gene in paraffin-embedded tissues and its clinicopathologic significance for synovial sarcoma

OBJECTIVE: To investigate the feasibility of detecting SYT-SSX fusion gene in paraffin-embedded tissues and its diagnostic significance for synovial sarcoma (SS). METHODS: Formalin-fixed, paraffin-embedded samples of 38 cases of SS and 40 cases of control tumors (including spindle cell sarcoma and metastatic adenocarcinoma) were retrived from archival materials. SYT-SSX fusion transcripts were detected in all samples by RT-PCR. House-keeping gene Porphobilinogen Deaminase (PBGD) was used to detect the quality of mRNA. RESULTS: PBGD mRNA was detected in 64 of the 78 tumor cases (82.1%). SYT-SSX fusion transcripts was detected in 33 of the 38 synovial sarcoma specimens. No SYT-SSX mRNA expression was found in control tumors. SYT-SSX mRNA expression rate reached 89.2% (33/37) in synovial sarcomas after exclusion of 1 case which was negative for both SYT-SSX and PBGD. In 33 SYT-SSX positive synovial sarcomas, 22 had SYT-SSX1 and 6 had SYT-SSX2 fusion transcripts. In 5 cases, the fusion type could not be distinguished. There was an association between SYT-SSX fusion type and histologic subtype. All 10 biphasic synovial sarcoma cases had the SYT-SSX1 fusion, whereas 12 of 18 monophasic synovial sarcoma had the SYT-SSX1 and 6 had the SYT-SSX2 fusion gene (P < 0.05). CONCLUSIONS: (1) Detection of SYT-SSX fusion gene in paraffin-embedded tissues was found to be a sensitive and specific method for the diagnosis and differential diagnosis of synovial sarcoma. (2) There was an association between SYT-SSX fusion type and histologic subtype.SYT-SSX2 fusion transcript could only be found in monophasic synovial sarcomas.