SS18 and synovial sarcoma: Such occurrences support the notion that the SSXRD domain, by mediating recruitment of transcriptional activators to induce Polycomb target genes during sarcomagenesis, is the key determinant of a synovial sarcoma signature, and that direct deregulation of the mSWI/SNF (BAF) complex through SS18 is not essential to all synovial sarcomas.