Characteristic for synovial sarcomas is the t(X;18)(p11.2;q11.2) translocation which is found in over 95% of all synovial sarcoma cases and results in the fusion of the SS18 (also called Syt) gene on chromosome 18 with one of the highly homologous SSX genes, SSX1, SSX2 or SSX4, on the X chromosome and consequently the expression of SS18-SSX fusion proteins [81]–[84]. This evidence concerns the gene SSX4 and synovial sarcoma.