title: Abdominal monophasic synovial sarcoma is a morphological and immunohistochemical mimic of gastrointestinal stromal tumour.
abstract: OBJECTIVE
  Synovial sarcomas may arise within retroperitoneal or pelvic tissues or, more rarely, within the luminal gastrointestinal tract. This case series aims to demonstrate how such primary abdominal synovial sarcomas may particularly mimic gastrointestinal stromal tumour (GIST) on both morphological and immunohistochemical grounds.
  
  
  RESULTS
  Four cases of primary abdominal synovial sarcoma were reviewed morphologically and with immunohistochemistry, fluorescence in-situ hybridization with an SS18 break-apart probe, and KIT/PDGFRA mutation analysis. The four patients comprised two males and two females, with a median age of 42 years (range: 17-59 years). Two synovial sarcomas arose within the stomach, one within the small-intestine mesentery, and the fourth within the retroperitoneum. All four tumours showed only a monophasic spindle cell component in the tissues available for review. All four tumours showed DOG1 immunopositivity, and three coexpressed CD117. Three tested cases did not show activating KIT or PDGFRA mutations, whereas all four cases showed chromosomal rearrangement of SS18.
  
  
  CONCLUSIONS
  A diagnosis of synovial sarcoma should be considered particularly if an abdominal spindle cell neoplasm shows a haemangiopericytomatous pattern and diffuse CD99 and CD56 immunopositivity. A confident distinction between abdominal synovial sarcoma and GIST requires KIT/PDGFRA mutation analyses and specific molecular testing for synovial sarcoma.
authors.affiliation: Department of Histopathology, Bristol Royal Infirmary, Bristol, UK.
authors.forename: Newton A C S
authors.initials: NA
authors.lastname: Wong
authors.affiliation: Department of Pathology, Royal Liverpool University Hospital, Liverpool, UK.
authors.forename: Fiona
authors.initials: F
authors.lastname: Campbell
authors.affiliation: Gloucestershire Cellular Pathology Laboratory, Cheltenham General Hospital, Cheltenham, UK.
authors.forename: Neil A
authors.initials: NA
authors.lastname: Shepherd
mesh_terms: D000293:Adolescent; D000328:Adult; D014408:Biomarkers, Tumor / Q000235:genetics / Q000276:immunology; D004252:DNA Mutational Analysis; D005260:Female; D005770:Gastrointestinal Neoplasms / Q000378:metabolism / Q000473:pathology*; D046152:Gastrointestinal Stromal Tumors / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D008875:Middle Aged; D009154:Mutation; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics / Q000378:metabolism*; D020797:Receptor, Platelet-Derived Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D013584:Sarcoma, Synovial / Q000378:metabolism / Q000473:pathology*; D055815:Young Adult
chemical_list: D014408:Biomarkers, Tumor; D019009:Proto-Oncogene Proteins c-kit; D020797:Receptor, Platelet-Derived Growth Factor beta
keywords: abdomen; diagnostic molecular pathology; gastrointestinal stromal tumours; histopathology; immunohistochemistry; synovial sarcoma