title: A challenging case of metastatic intra-abdominal synovial sarcoma with unusual immunophenotype and its differential diagnosis.
abstract: 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.
authors.affiliation: 1st Department of Pathology and Experimental Cancer Research, Semmelweis University, Budapest 1085, Hungary.
authors.forename: Yi-Che
authors.initials: YC
authors.lastname: Changchien
authors.forename: Uhrin
authors.initials: U
authors.lastname: Katalin
authors.forename: János
authors.initials: J
authors.lastname: Fillinger
authors.forename: László
authors.initials: L
authors.lastname: Fónyad
authors.forename: Gergő
authors.initials: G
authors.lastname: Papp
authors.forename: Ferenc
authors.initials: F
authors.lastname: Salamon
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Sápi