Are there geographical differences in the frequency of SYT-SSX1 and SYT-SSX2 chimeric transcripts in synovial sarcoma?

The impact of chromosomal translocation locus and fusion oncogene coding sequence in synovial sarcomagenesis

Synovial sarcomas are aggressive soft-tissue malignancies that express chromosomal translocation-generated fusion genes, SS18-SSX1 or SS18-SSX2 in most cases. Here, we report a mouse sarcoma model expressing SS18-SSX1, complementing our prior model expressing SS18-SSX2. Exome sequencing identified no recurrent secondary mutations in tumors of either genotype. Most of the few mutations identified in single tumors were present in genes that were minimally or not expressed in any of the tumors. Chromosome 6, either entirely or around the fusion gene expression locus, demonstrated a copy number gain in a majority of tumors of both genotypes. Thus, by fusion oncogene coding sequence alone, SS18-SSX1 and SS18-SSX2 can each drive comparable synovial sarcomagenesis, independent from other genetic drivers. SS18-SSX1 and SS18-SSX2 tumor transcriptomes demonstrated very few consistent differences overall. In direct tumorigenesis comparisons, SS18-SSX2 was slightly more sarcomagenic than SS18-SSX1, but equivalent in its generation of biphasic histologic features. Meta-analysis of human synovial sarcoma patient series identified two tumor-gentoype-phenotype correlations that were not modeled by the mice, namely a scarcity of male hosts and biphasic histologic features among SS18-SSX2 tumors. Re-analysis of human SS18-SSX1 and SS18-SSX2 tumor transcriptomes demonstrated very few consistent differences, but highlighted increased native SSX2 expression in SS18-SSX1 tumors. This suggests that the translocated locus may drive genotype-phenotype differences more than the coding sequence of the fusion gene created. Two possible roles for native SSX2 in synovial sarcomagenesis are explored. Thus, even specific partial failures of mouse genetic modeling can be instructive to human tumor biology.

The clinical implication of SS18-SSX fusion gene in synovial sarcoma

Background:

The aim of this study is to evaluate distribution and clinical impact of the SS18-SSX fusion gene in patients with synovial sarcoma in China.

Methods:

We collected and analysed the clinical data of 88 patients using univariate and multivariate survival analysis. HEK 293T and NIH 3T3 cell lines were transfected with the SS18-SSX1 or SS18-SSX2 gene to determine the respective involvement of these fusion genes in cell proliferation and invasion.

Results:

Overall survival was significantly better among SS18-SSX2 cases (P=0.001), FNCLCC grade 2 cases (P<0.001), and UICC stage 1 or 2 (P<0.001) by univariate and multivariate survival analysis. SS18-SSX1-positive cells were more proliferative and invasive than SS18-SSX2-positive cells.

Conclusion:

SS18-SSX fusion type is a significant prognostic factor for patients with synovial sarcoma.

Prognostic implication of SYT-SSX fusion type and clinicopathological parameters for tumor-related death, recurrence, and metastasis in synovial sarcoma

The present study aimed to describe the distribution and features of the SYT-SSX fusion gene in Chinese patients with synovial sarcoma (SS), and to analyze the prognostic value of SYT-SSX fusion type and clinicopathological parameters for tumor-related death, recurrence, and metastasis in SS. SYT-SSX1 and SYT-SSX2 fusion transcripts were tested by reverse transcription-polymerase chain reaction in 141 formalin-fixed, paraffin-embedded SS. The prognostic implication of SYT-SSX fusion type and clinicopathological parameters were analyzed by univariate and multivariate survival analyses. SYT-SSX1 and SYT-SSX2 were detected in 50 (34.5%) and 91 (64.5%) tumors, respectively. SYT-SSX1 (risk ratio [RR] = 2.032, P = 0.004), larger tumor size (RR = 1.859, P = 0.008), and aggressive Fédération Nationale des Centers de Lutte Contre le Cancer grade (RR = 2.094, P = 0.001) were adverse predictors for disease-specific survival. However, SYT-SSX fusion type was not associated with local recurrence-free survival (P = 0.216). Patients with larger tumors (RR = 2.071, P = 0.005) and those who received marginal excision (RR = 2.556, P = 0.005) had poor local recurrence-free survival. Besides, SYT-SSX1 (RR = 1.859, P = 0.037), older age (RR = 1.799, P = 0.040), and aggressive International Union Against Cancer stage (RR = 3.690, P < 0.001) proved to be adverse prognostic factors for metastasis-free survival. In conclusion, compared to SYT-SSX1, SYT-SSX2 was more frequent in Chinese patients with SS. Moreover, SYT-SSX1 was an adverse predictor for disease-specific survival and metastasis-free survival, but had no relation to local recurrence-free survival. In addition, histological grade and tumor size were also important prognostic factors for SS.