Synovial sarcoma is one of the rarest forms of soft tissue sarcoma.  It most frequently arises near the joints of the arms, neck or legs in adolescents and young adults.  Most cases are associated with a reciprocal t(x;18)(p11.2;q11.2) translocation between the SS18 gene on chromosome 18 and one of three SSX genes (SSX1, SSX2 and SSX4) on the X chromosome.  The resulting fusion protein is thought to contribute to pathogenesis by bringing together the transcriptional activating domain of SS18 and the transcriptional repressor domains of SSX, and incorporating into the SWI/SNF chromatin remodelling complex, blocking its tumour suppressor function. 

A positive SS18 gene rearrangement result is considered to be supportive evidence where a pathological diagnosis of synovial sarcoma is being considered.

SS18 gene rearrangements are detected by break-apart fluorescence in-situ hybridisation (FISH) analysis.  The method will identify a chromosomal rearrangement involving the SS18 locus at 18q11.2, but not the specific gene fusion partner.

For clinical advice on appropriate investigations, please contact our Molecular Pathology team.