SS18-SSX Rearrangement in Synovial Sarcoma Using Fluorescent in Situ Hybridization: A Report from an Iranian Population and Literature Review

Background: synovial sarcoma is an aggressive soft tissue sarcoma. it has a wide spectrum of histopathologic patterns and uncertain immunohistochemistry, rendering it a diagnostic challenge. the objective of this study was to investigate the diagnostic utility and impact of ss18-ssx rearrangement evaluation in an iranian population previously diagnosed with synovial sarcoma without such molecular tests. method: we conducted this cross-sectional study on 44 formalin-fixed paraffin- embedded tissue blocks obtained from 23 synovial sarcoma patients (males, 69%; mean age, 36.4 years) and 11 cases with other neoplasms as negative controls. we assessed these specimens for ssx-ss18 gene rearrangement by break-apart fluorescent in situ hybridization (fish) probes. results: fish study showed ss18-ssx fusion gene in 17 (73.91%) cases while six (26.09%) cases and negative controls did not show ss18-ssx fusion. histopathologic type of tumor was significantly related to the presence of rearrangement (p=0.002) (rearranged: 11 biphasic and six monophasic tumors; non-rearranged: three monophasic and three poorly-differentiated tumors). conclusion: this study supports the idea that molecular studies contribute to the confirmation of synovial sarcoma diagnosis, particularly in monophasic and poorlydifferentiated subtypes, which show vague immunohistochemical results.