The Value of SS18-SSX,SOX-2 and PAX-7 antibodies in the pathological diagnosis of synovial sarcoma

ZHONG Ling-ling; XIAN Li-ying; TANG Fang; WEI Zong-chen; LIU Xiao-fen; HUANG Gao-xiang

doi:10.3969/j.issn.1007-8096.2023.09.003

Abstract：Objective To investigate the roles of SS18-SSX,SOX-2 and PAX-7 antibodies in the differential diagnosis of synovial sarcoma(SS).Methods The FFPE surgical tumor specimen from 11 genetically-confirmed SS and 32 morphological mimics were selected and the immunohistochemical staining was used to detect the SS18-SSX,SOX-2 and PAX-7 protein expression in the whole section of these specimen.Results SS18-SSX immunostaining was found diffusely positive in all SS,but negative in all morphological mimics(P＜0.05).SOX-2 immunostaining was positive in 4 biphasic SS and 1 monophasic fibrous SS,whereas SOX-2 immunostaining was positive in 2 morphological mimics(P＞0.05).PAX-7 immunostaining was positive in 5 biphasic SS and negative in 6 non-biphasic SS,whereas PAX-7 immunostaining was positive in 1 morphological mimics(P＞0.05).Of note,PAX-7 expression was diffusely weak or moderate positive in the epithelial component of biphasic SS,but negative in majority of spindle tumor cells.Although SOX-2 immunostaining was found in both epithelial and spindle components of SS,its expression was more extensive and stronger in the epithelial and glandular tumor cells than spindle tumor components.Conclusion The high sensitivity and specificity of SS18-SSX fusion-specific antibody can be applied in the pathological diagnosis in majority of SS without the molecular pathological detection.The SOX-2 and PAX-7 immunostaining present a special pattern in the biphasic synovial sarcoma,and therefore they can be combined and used to classify the morphological variant in equivocal SS cases.