SSX4 and synovial sarcoma: Almost all patients with SS harbor an aberrant chromosomal translocation that fuses the two genes, namely, SS translocation chromosome 18 (SS18, also known as SMARCL1, SYT, and SSXT) located in the chromosome 18q11 and one of the SSX family genes in the chromosome Xp11 (either SSX1, SSX2, or SSX4), producing a class of SS-specific onco-fusions termed SS18::SSX (1, 6, 7).