title: Clinical Neuropathology practice guide 6-2013: morphology and an appropriate immunohistochemical screening panel aid in the identification of synovial sarcoma by neuropathologists.
abstract: OBJECTIVE
  Pathologists are under increasing pressure to accurately subclassify sarcomas, yet neuropathologists have limited collective experience with rare sarcoma types such as synovial sarcoma. We reviewed 9 synovial sarcomas affecting peripheral nerve diagnosed by neuropathologists and explored the morphologic and immunohistochemical differences between these and MPNST. Our goal was to make practical recommendations for neuropathologists regarding which spindle cell tumors affecting nerve should be sent for SYT-SSX testing.
  
  
  METHODS
  Clinical records and genetics were reviewed retrospectively and central pathology review of 9 synovial sarcomas and 6 MPNST included immunohistochemistry for SOX10, S100, BAF47, CK (lmw, pan, CK7, CK19), EMA, CD34, bcl2, CD99, and neurofilament.
  
  
  RESULTS
  Common synovial sarcoma sites were brachial plexus, spinal and femoral nerve, none were "intra-neural", all had the SYTSSX1 translocation, and 6/9 were monophasic with myxoid stroma and distinct collagen. Half of the monophasic synovial sarcomas expressed CK7, CK19 or panCK in a "rare positive cells pattern", 8/9 (89%) expressed EMA, and all were SOX10 immunonegative with reduced but variable BAF47 expression.
  
  
  CONCLUSIONS
  We recommend that upon encountering a cellular spindle cell tumor affecting nerve neuropathologists consider the following: 1) SYT-SSX testing should be performed on any case with morphology suspicious for monophasic synovial sarcoma including wiry or thick bands of collagen and relatively monomorphous nuclei; 2) neuropathologists should employ a screening immunohistochemical panel including one of CK7, panCK or CK19, plus EMA, S100 and SOX10, and 3) SYT-SSX testing should be performed on any spindle cell tumor with CK and/or EMA immunopositivity if SOX10 immunostaining is negative or only labels entrapped nerve elements.
authors.forename: Julia Lee
authors.initials: JL
authors.lastname: Keith
authors.forename: Juan
authors.initials: J
authors.lastname: Bilbao
authors.forename: Sidney
authors.initials: S
authors.lastname: Croul
authors.forename: Lee Cyn
authors.initials: LC
authors.lastname: Ang
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Guiot
authors.forename: John
authors.initials: J
authors.lastname: Rossiter
authors.forename: Zeina
authors.initials: Z
authors.lastname: Ghorab
authors.forename: Cynthia
authors.initials: C
authors.lastname: Hawkins
authors.forename: Jason
authors.initials: J
authors.lastname: Karamchandani
mesh_terms: D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000032:analysis; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D010524:Peripheral Nervous System Neoplasms / Q000145:classification / Q000175:diagnosis*; D017410:Practice Guidelines as Topic; D013584:Sarcoma, Synovial / Q000145:classification / Q000175:diagnosis*
chemical_list: D014408:Biomarkers, Tumor