198 Development, validation and concordance of two MAGE-A4 immunohistochemistry (IHC) assays to establish prognostic value of MAGE-A4 expression in synovial sarcoma by Dennis Williams, Elizabeth Ross, Armelle Dufresne, Nicolas Gadot, Marian Van Kerckhoven, Robert Connacher, Konstantinos Avraam, Mary Schneck, Sofie Van Rossom, Tianjiao Wang