Association of SYT-SSX fusion types with proliferative activity and prognosis in synovial sarcoma

The t(X;18)(p11.2;q11.2) translocation commonly found in synovial sarcoma (SS) results in the fusion of the SYT gene on chromosome 18 to either of two closely related genes, SSX1 and SSX2, on chromosome X. It has been suggested that patients who have SS bearing SYT-SSX1 fusion have worse prognosis than those bearing SYT-SSX2 fusion. However, little is known about the biologic basis or the relationship with the histopathologic risk factors in regard to the different fusion types. We analyzed 19 cases of SS with no metastasis at diagnosis. These tumors were classified by reverse transcription-polymerase chain reaction to SYT-SSX1 and SYT-SSX2 types. The expression of Ki-67, p27, p53, and bcl-2 and various clinicopathologic parameters including mitotic rate were compared between the two fusion types. The SYT-SSX1 type fusion was associated with high Ki-67 expression (P = .011) and high mitotic rate (P = .070). No significant differences were found between the two types as to the expression of p27, p53, and bcl-2 and other clinicopathologic parameters. The survival analysis showed that SYT-SSX1-type fusion, high Ki-67 expression, and high mitotic rate correlated with shorter metastasis-free survival. These data suggested that SYT-SSX fusion type is associated with tumor cell proliferative activity and prognosis of patients who have SS.