Synovial sarcoma with ossification and calcification with SS18 immunochemical expression and rearrangement by fluorescent in situ hybridization

Abstract

Synovial sarcoma is a soft tissue tumor of uncertain origin. Generally, it is a monophasic spindle cell neoplasm that can have glandular-like structures. Ossification and presence of calcification is a rare phenomenon with only a few reported cases. We present the case of a young male with a synovial sarcoma of the right foot. Histology revealed prominent deposits of tumoral osteoid and coarse calcifications. The diagnosis was confirmed by the expression of SS18 by immunohistochemistry and the demonstration of the rearrangement of the SS18 gene by fluorescent in situ hybridization. We reviewed the literature for synovial sarcoma with prominent ossification or calcification, and to the best of our knowledge, this is the first case with expression of SS18 by immunohistochemistry. The main differential diagnoses are osteosarcoma (both primary of bone and extraosseous) and sclerosing epithelioid fibrosarcoma.

Keywords: Fibrosarcoma epitelioide esclerosante; Inmunohistoquímica SS18; Ossifying synovial sarcoma; Osteosarcoma; SS18 immunochemistry; Sarcoma sinovial; Sarcoma sinovial con calcificaciones; Sarcoma sinovial osificante; Sclerosing epithelioid fibrosarcoma; Synovial sarcoma; Synovial sarcoma with calcification.