demonstrated that a novel SS18::SSX fusion-specific antibody is highly sensitive and specific in the diagnosis of synovial sarcomas when used in IHC, with the SS18::SSX antibody having a sensitivity of 95% and specificity of 100% and an antibody to the SSX C-terminus is also highly sensitive but slightly less specific, the SSX C-terminus antibody exhibiting a sensitivity of 100% and specificity of 96%. This evidence concerns the gene SS18 and synovial sarcoma.