SS18 and synovial sarcoma: In synovial sarcoma a recurrent chromosomal translocation fuses the SS18 gene (a subunit of the SWI/SNF chromatin remodeling complex [10]) on chromosome 18 to one of three related genes on the X chromosome, SSX1, SSX2 and rarely SSX4, resulting in the expression of a SS18-SSX fusion protein [11–16].