Primary superficial synovial sarcoma: clinical and histopathological characteristics in eight cases with molecular confirmation

Background and Aims: Synovial sarcoma (SS) is a spindled cell sarcoma demonstrating varying degrees of epithelial differentiation and characterized by a pathognomonic t(X;18) translocation. SS most frequently involves deep soft tissue of the extremities in young adults. Superficial SS involving dermis and/or subcutaneous tissue is exceedingly rare. Methods and results: We identified eight cases of primary superficial synovial sarcomas across three tertiary institutions. All cases were confined to the dermis/subcutis based on imaging or gross and microscopic examination. The average patient age was 36 years (range 14-50). The average tumor size was 2.4 cm (range 0.9-3.9 cm) and lesions showed classic monophasic (n = 4) or biphasic (n = 4) morphology. All tumors expressed keratin AE1/AE3 and/or epithelial membrane antigen (EMA), but were negative for CD34. The diagnosis for each case was confirmed by molecular detection of t(X;18). Six of the eight cases were treated with curative excision while the other two received additional radiotherapy. Follow-up was available for six patients (mean 68 months, range 2-108 months) and no patient experienced recurrence or metastatic disease. Conclusions: We present the largest series to date of primary superficial SS with molecular confirmation for all cases. SS should be considered when evaluating a cutaneous monomorphic spindle cell neoplasm.