Key clinical point: SS18-SSX gene fusion and its downstream targets SOX2 and Histone H3 (H3K27me3) are important in synovial sarcoma, a finding that strengthens the notion that synovial sarcoma is driven by epigenetic processes similar to those operating in pluripotent stem cells.

Main finding: SOX2 reactivity was detectable in 35 synovial sarcoma cases (58.3%). Only 13 cases of the other 343 soft tissue tumors, varying from nodular fasciitis to undifferentiated pleomorphic sarcoma, expressed SOX2, and 12 of the 13 of these were undifferentiated high grade sarcoma. H3K27me3 immunohistochemistry of the synovial sarcoma cases revealed a high statistically significant correlation between SOX2 and H3K27me3 expression (P less than .0005). Similar to SOX2, H3K27me3 expression was not correlated with tumor grade. Six SOX2 positive synovial sarcoma cases were analyzed by FISH, and none of these cases revealed an amplification of the SOX2 gene.

Study details: In total, 60 samples of synovial sarcomas from the reference center for soft tissue tumors at the institute of pathology of the Jena University hospital were included into the study along with 343 other tissue tumors. Protein analysis was done by immunohistochemistry of tissue microarrays. All synovial sarcoma cases were confirmed by molecular testing using SS18 FISHbreak apart probes.

Disclosures: The authors had no relevant financial disclosures.

Source: Zayed H and Petersen I. Pathology--Research and Practice 2018: 214; 1000-1007. https://doi.org/10.1016/j.prp.2018.05.004