Synovial sarcomas account for 7% to 10% of all human soft-tissue sarcomas. The tumors arise at any age, but affect mainly young adults and more commonly males. Clinically, they appear as deep-seated slowly growing masses. In more than half of the cases, metastases develop, primarily to the lungs but also to the lymph nodes and bone marrow. A specific translocation, t(X; 18)(p11.2; q11.2), is found in more than 90% of reported synovial sarcoma, including biphasic, monophasic, and poorly differentiated tumors. The breakpoints of the t(X; 18) have been cloned and shown to involve the fusion of the SYT gene at 18q11 to either of two highly homologous genes at Xp11 called SSX1 and SSX2. The SYT-SSX1 fusion is associated with biphasic morphology and a worse prognosis, whereas the SYT-SSX2 fusion tends to show monophasic morphology and better outcome.
