title: Carbonic anhydrase IX (CAIX) does not differentiate between benign and malignant mesothelium.
abstract: OBJECTIVE
  To examine carbonic anhydrase IX (CAIX), a marker of renal cell carcinoma that recently has been described in malignant effusions.
  
  
  METHODS
  Pleural and peritoneal fluids with the following diagnoses-reactive (n = 23), carcinoma (n = 17), and "suspicious for mesothelioma" (n = 4)-were immunostained for CAIX, calretinin, Ber-EP4, and MOC31. A tissue microarray of epithelioid (n = 27) and sarcomatoid (n = 8) mesotheliomas and three cases of benign mesothelium were also immunostained for CAIX.
  
  
  RESULTS
  Mesothelial cells in both reactive (18/23) and malignant effusions (18/21) were positive for CAIX (P > .05). In carcinomatous effusions, CAIX expression was restricted to the mesothelial cells. Agreement between CAIX and calretinin expression was present in 89% of cases. In tissues, CAIX was positive in 100% of benign and 91% of malignant mesothelium.
  
  
  CONCLUSIONS
  CAIX can be a useful ancillary marker for identifying mesothelial cells. There is no difference in CAIX expression between benign and malignant mesothelium. Caution should be exercised while evaluating for metastasis from renal cell carcinoma.
authors.affiliation: From the Department of Pathology, University of Chicago, Chicago, IL, and.
authors.forename: Vijayalakshmi
authors.initials: V
authors.lastname: Ananthanarayanan
authors.affiliation: Department of Pathology, University of Washington, Seattle.
authors.forename: Maria
authors.initials: M
authors.lastname: Tretiakova
authors.affiliation: From the Department of Pathology, University of Chicago, Chicago, IL, and.
authors.forename: Aliya N
authors.initials: AN
authors.lastname: Husain
authors.affiliation: From the Department of Pathology, University of Chicago, Chicago, IL, and Department of Pathology, University of Washington, Seattle.
authors.forename: Thomas
authors.initials: T
authors.lastname: Krausz
authors.affiliation: From the Department of Pathology, University of Chicago, Chicago, IL, and tatjana.antic@uchospitals.edu.
authors.forename: Tatjana
authors.initials: T
authors.lastname: Antic
mesh_terms: D000951:Antigens, Neoplasm / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000378:metabolism; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases / Q000378:metabolism*; D002292:Carcinoma, Renal Cell / Q000175:diagnosis* / Q000378:metabolism / Q000556:secondary; D004848:Epithelium / Q000378:metabolism* / Q000473:pathology; D005260:Female; D006801:Humans; D007680:Kidney Neoplasms / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008654:Mesothelioma / Q000175:diagnosis / Q000378:metabolism / Q000473:pathology; D009362:Neoplasm Metastasis / Q000175:diagnosis* / Q000473:pathology; D016066:Pleural Effusion, Malignant / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology
chemical_list: D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases
keywords: Cytopathology; Immunopathology; Pulmonary