Abstract: Objective To explore the pathological characteristics and differential diagnosis of synovial sarcoma, so as to improve the understanding and diagnosis of this sarcoma. MethodsRetrospective analysis was performed using data from six patients with synovial sarcoma. The morphological and immunohistochemical characteristics were observed, while related literature was reviewed. ResultsFor these synovial sarcoma patients, the primary site was the lungs (3 cases), the knee joint (2 cases) and planta pedis (1 case). There were 2 cases of bipolar differentiation and 4 cases of single-phase fiber differentiation. For the bipolar synovial sarcoma, positive expression was found for cytokeratin (CK), epithelial membrane antigen (EMA), transducin-like enhancer protein 1 (TLE-1), E-cadherin and vimentin to various degrees, in addition to positive expression of smooth muscle actin (SMA) and CD34 in 1 case and negative expression of S-100 and desmin in both cases. For the single-phase fibrous synovial sarcomas, there were positive expression of vimentin and Bcl-2 in all cases, positive CK, EMA and CD99 in 2 cases, positive calponin in 3 cases, positive S-100 and SMA in 1 case and negative desmin, CD34, TTF-1 in all cases. The positive Ki-67 labeling index ranged from 10% to 60%. ConclusionsSynovial sarcoma has morphological diversity through microscopy, which can differentiate towards the epithelial and fiber and need to be distinguished from fibrosarcoma, metastatic adenocarcinoma, spindle-shaped carcinoma. Diagnosis depends on both tissue morphology and immunohistochemistry, while molecular genetic testing may be carried out when necessary.