title: Gastrointestinal Kaposi's sarcoma: CD117 expression and the potential for misdiagnosis as gastrointestinal stromal tumour.
abstract: OBJECTIVE
  Gastrointestinal Kaposi's sarcoma (KS) may mimic gastrointestinal stromal tumours (GISTs) histologically. Studies have shown that KS outside the gastrointestinal (GI) tract may express CD117, an antibody usually used to support a diagnosis of GIST. The aim was to evaluate the clinicopathological features of GI KS, including the expression of CD117 with and without antigen retrieval.
  
  
  RESULTS
  Fourteen GI KS were assessed histologically, 12 of which were also subjected to immunohistochemistry for CD34, human herpesvirus (HHV) 8, DOG1 and CD117. CD117 immunohistochemistry was performed with and without antigen retrieval. All cases showed an infiltrative spindle cell tumour. Lamina propria infiltration, lymphoplasmacytic inflammation, extravasated red blood cells and haemosiderin were typical histological features. In all cases tumour cells were positive for CD34 and HHV8, but negative for DOG1. CD117 was positive in four of 12 cases without antigen retrieval and 10 of 12 cases with antigen retrieval.
  
  
  CONCLUSIONS
  The microscopic distinction of GI KS from GIST can be difficult. Clues that raise the possibility of GI KS include young patient age, a history of immunosuppression, lamina propria infiltration, lymphoplasmacytic inflammation, extravasated red blood cells and haemosiderin deposition. Use of the immunomarkers CD117 (without antigen retrieval), HHV8 and DOG1 may aid in the distinction between GI KS and GIST.
authors.affiliation: Department of Pathology, London Health Sciences, London, Ontario, Canada.
authors.forename: J R
authors.initials: JR
authors.lastname: Parfitt
authors.forename: M
authors.initials: M
authors.lastname: Rodriguez-Justo
authors.forename: R
authors.initials: R
authors.lastname: Feakins
authors.forename: M R
authors.initials: MR
authors.lastname: Novelli
mesh_terms: D000328:Adult; D000075369:Anoctamin-1; D014408:Biomarkers, Tumor / Q000378:metabolism; D018118:Chloride Channels; D003937:Diagnosis, Differential; D003951:Diagnostic Errors; D005260:Female; D005770:Gastrointestinal Neoplasms / Q000175:diagnosis / Q000378:metabolism*; D046152:Gastrointestinal Stromal Tumors / Q000175:diagnosis / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000378:metabolism; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism*; D012514:Sarcoma, Kaposi / Q000175:diagnosis / Q000378:metabolism*; D014764:Viral Proteins / Q000378:metabolism
chemical_list: C476213:ANO1 protein, human; D000075369:Anoctamin-1; D014408:Biomarkers, Tumor; D018118:Chloride Channels; C403495:KS-SM protein, Human herpesvirus 8; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D014764:Viral Proteins; D019009:Proto-Oncogene Proteins c-kit