{"entity":{"id":"ss18-ssx-fusion","kind":"term","name":"SS18::SSX fusion (synovial sarcoma)","aka":["SS18-SSX","SS18::SSX1","SS18::SSX2","SS18::SSX4","SYT-SSX","SYT::SSX","t(X;18)","t(X;18)(p11;q11)","SS18-SSX antibody","SS18-SSX immunohistochemistry","synovial sarcoma fusion","TLE1"],"tldr":"Every true synovial sarcoma carries a fusion between the SS18 gene on chromosome 18 and an SSX gene on the X chromosome; finding it by FISH, RNA sequencing or a newer antibody stain confirms a diagnosis that pathologists otherwise struggle with, and it also flags the tumour for the MAGE-A4 and NY-ESO-1 cell therapies that work almost only in this disease.","summary":"What is measured: the SS18::SSX fusion from t(X;18)(p11;q11). How: FISH with an SS18 break-apart probe, RT-PCR or targeted RNA sequencing naming the partner (SSX1 in about two-thirds, SSX2 in a third, SSX4 rarely), or immunohistochemistry with the fusion-specific SS18-SSX antibody (about 95 percent sensitive and near 100 percent specific) and the SSX C-terminus antibody; TLE1 staining is a sensitive but less specific screen. The fusion protein hijacks the BAF (SWI/SNF) chromatin-remodelling complex and displaces SMARCB1, which is why the tumours are partly INI1-deficient; a poorly differentiated component and size over 5 cm worsen the outlook. About 70 percent express MAGE-A4 and 80 percent NY-ESO-1, cancer-testis antigens. What a result changes: it settles the diagnosis against MPNST, solitary fibrous tumour, Ewing sarcoma and poorly differentiated carcinoma; synovial sarcoma is more chemosensitive than most sarcomas (ifosfamide with doxorubicin); with MAGE-A4 immunohistochemistry and HLA-A*02 typing it qualifies patients for afamitresgene autoleucel (approved 2024) and NY-ESO-1-directed letetresgene autoleucel; BRD9 degraders and other BAF-directed drugs are in trials. Where it matters: synovial sarcoma.","asOf":"2026-09-17","links":[],"tags":[],"related":["gene-fusion","fish","rna-seq","ihc","mage-a4","hla-a02-restriction","afamitresgene-autoleucel","ifosfamide","doxorubicin"],"cancers":["synovial-sarcoma"],"sections":[],"technologies":[],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"category":"Biomarkers"},"route":"/terms/ss18-ssx-fusion/","neighbours":{"term":[{"id":"fish","kind":"term","name":"FISH / ISH (in situ hybridisation)","route":"/terms/fish/"},{"id":"gene-fusion","kind":"term","name":"Gene fusion","route":"/terms/gene-fusion/"},{"id":"hla-a02-restriction","kind":"term","name":"HLA-A*02:01 restriction","route":"/terms/hla-a02-restriction/"},{"id":"ihc","kind":"term","name":"Immunohistochemistry (IHC)","route":"/terms/ihc/"}],"technology":[{"id":"rna-seq","kind":"technology","name":"RNA sequencing & expression profiling","route":"/technologies/rna-seq/"}],"target":[{"id":"mage-a4","kind":"target","name":"MAGE-A4","route":"/targets/mage-a4/"}],"drug":[{"id":"afamitresgene-autoleucel","kind":"drug","name":"Afamitresgene autoleucel","route":"/drugs/afamitresgene-autoleucel/"},{"id":"doxorubicin","kind":"drug","name":"Doxorubicin","route":"/drugs/doxorubicin/"},{"id":"ifosfamide","kind":"drug","name":"Ifosfamide","route":"/drugs/ifosfamide/"}],"cancer":[{"id":"marginal-zone-lymphoma","kind":"cancer","name":"Marginal zone lymphoma","route":"/cancers/marginal-zone-lymphoma/"},{"id":"synovial-sarcoma","kind":"cancer","name":"Synovial sarcoma","route":"/cancers/synovial-sarcoma/"}]}}