SSX4 and synovial sarcoma: The characteristic and specific translocation t(X;18((p11.2q11.2)) of human SS causes the fusion of the SS18 (also known as SYT) gene on chromosome 18 to SSX1, SSX2 or, rarely, SSX4 on chromosome X at Xp11.2, and contributes to the formation of SS18-SSX fusion transcripts, regardless of histologic subtype [4–7].