In both cases, reverse transcription-polymerase chain reaction using ribonucleic acid extracted from formalin-fixed, paraffin-embedded tissues detected SYT-SSX2 fusion gene transcripts, which are characteristic molecular findings of synovial sarcoma.
Real-time RT-PCR assays specific for Ewing's sarcoma (EWS-FLI1, EWS-ERG, EWS-ETV1, EWS-ETV4, and EWS-FEV), synovial sarcoma (SYT-SSX1 and SYT-SSX2), and rhabdomyosarcoma (PAX3-FKHR and PAX7-FKHR) were tested across the samples.
The t(X;18)(p11.2;q11.2), which results in fusion of the SYT gene at 18q11 with the SSX1, SSX2, or (rarely) SSX4 gene is a primary genetic event in 90% of SS.
The presence of an SYT-SSX gene fusion resulting from the t(X;18) characteristic of synovial sarcoma was demonstrated by reverse transcriptase polymerase chain reaction in three of three tumors in which adequate RNA could be obtained from paraffin blocks.
This finding suggests that this novel fusion gene, which involves exon 6 of SSX only, is sufficient to keep the transforming function conferred by the SYT/SSX translocation of SS.
This involved blind analysis of two negative sarcoma samples and three synovial sarcomas in which corresponding frozen material had been previously shown to have the translocation involving different SSX genes.
Here we report a case of synovial sarcoma with a novel form of the SYT-SSX2 fusion transcript, in which 75 bases were inserted at the common fusion junction.
Synovial sarcoma is characterized cytogenetically by an X;18 translocation [t (X;18) (p11;q11)] that results in the fusion of the SYT gene from chromosome 18 to either of two highly homologous genes at Xp11, SSX1 or SSX2.
Apart from the canonical SS18-SSX fusion, this is only the second alternative gene fusion variant described in synovial sarcoma to date, in addition to two cases harboring the SS18L1-SSX1 fusion.
The demonstration of characteristic sequences at the SYT-SSX breakpoint regions is expected to improve our understanding of the molecular genetic mechanisms behind translocations in general, and of the SYT-SSX fusions in synovial sarcoma in particular.
In conclusion, the SYT-SSX fusion type is not a significant prognostic factor unlike tumor size, followed by histological grade for patients with localized synovial sarcoma in Japan.
As a result of the synovial sarcoma associated t(X;18) translocation, the human SYT gene on chromosome 18 is fused to either the SSX1 or the SSX2 gene on the X chromosome.
Our new FISH assay has several advantages, including its applicability to paraffin-embedded samples, discrimination of the SS18-SSX1 and SS18-SSX2 translocations particularly in cases with aneuploidy, and potentially detecting translocations in all cases of synovial sarcoma, even with variant translocations.
A characteristic SYT-SSX fusion gene resulting from the chromosomal translocation t(X;18)(p11;q11) is detectable in almost all synovial sarcomas, a malignant soft tissue tumor widely believed to originate from as yet unidentified pluripotent stem cells.
Sequence analysis revealed that one of these antigens, HOM-MEL-40, was coded for by the SSX2 gene, which has recently been described to be involved in the t(X;18) translocation of human synovial sarcomas.
This study was performed to analyze the expression of MAGE by immunohistochemistry with mAb 57B in 25 synovial sarcomas (12 monophasic, 13 biphasic), which were typed for the t(X;18)-derived fusion transcript by reverse transcriptase polymerase chain reaction (19 SYT-SSX1, 6 SYT-SSX2).
With this method, 27 tumors (9 synovial sarcomas and 18 nonsynovial sarcomas) were studied and showed SYT-SSX1 rearrangement in 6 cases and SYT-SSX2 in 3 cases.