Real-time reverse transcription-polymerase chain reaction for detection of SYT-SSX translocation in synovial sarcoma

Abstract

9553 Background: Synovial sarcoma is the most common non-rhabdomyosarcomatous soft tissue sarcoma in children and adolescents. A specific translocation, t(X;18), induces fusion of the SYT gene on chromosome 18 to an SSX gene on chromosome X. The resulting fusion gene consists of at least 2 subtypes with different breakpoints: SYT-SSX1(X;18)(p11.23;q11.2) and SYT-SSX2 (X;18)(p11.21;q11.2). Because t(X;18) transcripts occur in >90% of synovial sarcoma subtypes, this marker may be useful for diagnosis. We evaluated the accuracy of a multiplex real-time reverse transcription-polymerase chain reaction (RT-PCR) assay for detection of the primary SYT-SSX fusion transcript types in formalin-fixed, paraffin-embedded (FFPE) tissues and frozen tissues. Methods: 17 tumors (7 synovial sarcomas, 4 Ewing’s sarcomas, 5 rhabdomyosarcomas, 1 small round blue-cell tumor), 4 normal tissues, and 4 control samples were tested for SYT-SSX translocations using real-time RT-PCR. Results were compared to those obtained with gel electrophoresis detection of amplified transcripts; discrepant results were confirmed by sequencing. Results: Concordance between real time RT-PCR and gel electrophoresis was 100% (25/25) for internal control genes and SYT-SSX1, and 92% (23/25) for SYT-SSX2. Of the 2 samples with discordant SYT-SSX2 results, 1 was positive by real-time RT-PCR but not gel electrophoresis and 1 was positive by electrophoresis but not real-time RT-PCR; in both cases, DNA sequencing confirmed the real-time RT-PCR results. The minimum percentage of tumor to normal cells required for detection of SYT-SSX fusion transcripts by real-time RT-PCR was 6.25%. Conclusions: This real-time RT-PCR assay appears to provide greater accuracy than gel electrophoresis for identification of SYT-SSX translocation and fusion types. No significant financial relationships to disclose.