Abstract: Synovial sarcoma is a malignant soft tissue neoplasm that can closely mimic carcinoma by histology and immunohistochemistry, making accurate diagnosis challenging in small or superficial biopsies. In this study, we report a rare case of a superficial biphasic synovial sarcoma with striking neuroendocrine differentiation, a biopsy of which was initially interpreted as a poorly differentiated carcinoma due to diffuse cytokeratin and neuroendocrine marker expression. Resection subsequently revealed a biphasic morphology, and molecular testing confirmed the presence of an SS18::SSX fusion, confirming the diagnosis of synovial sarcoma. This case highlights a potential diagnostic pitfall in dermatopathology and stresses the importance of confirmatory molecular testing in cases where both sarcoma and carcinoma are included in the differential diagnosis.
Phillipow et al. (Fri,) studied this question.