A Challenging Case of Metastatic Intra-Abdominal Synovial Sarcoma with Unusual Immunophenotype and Its Differential Diagnosis

الملخص EN

The primary and metastatic gastrointestinal synovial sarcoma is rare with a wide differential diagnosis.

It usually expresses cytokeratins EMA, BCL2 with an occasional CD99, and S100 positivity but not desmin.

We present a case of metastatic synovial sarcoma with unusual immunophenotype causing diagnostic challenges.

The tumor cells showed focal cytokeratin, EMA, and, unexpectedly, desmin positivity.

Additional intranuclear TLE-1 positivity and negativity for CD34 and DOG-1 were also identified.

A diagnosis of monophasic synovial sarcoma was confirmed by using FISH break-apart probe.

RT-PCR revealed the SYT-SSX1 fusion gene.

Intra-abdominal synovial sarcoma, either primary or metastatic, with unusual desmin positivity raises the diagnostic challenge, since a wide range of differential diagnoses could show a similar immunophenotype (leiomyosarcoma, desmoid tumor, myofibroblastic tumor, and rarely GIST etc.).

Typical morphology and focal cytokeratin/EMA positivity should alert to this tumor, and FISH and RT-PCR remain the gold standard for the confirmation.