title: Calretinin staining pattern aids in the differentiation of mesothelioma from adenocarcinoma in serous effusions.
abstract: BACKGROUND
  The differentiation between malignant mesothelioma and adenocarcinoma based on morphology alone can be a diagnostic challenge. The majority of the available antibodies recognize molecules expressed by adenocarcinoma whereas to the authors' knowledge specific markers for mesothelial cells are lacking. Calretinin, a calcium-binding protein, has been reported to be a selective marker for mesothelioma and largely is absent from adenocarcinoma on histologic material. The results with cytologic preparations have been inconsistent.
  
  
  METHODS
  To evaluate the specificity of calretinin in differentiating mesothelioma from adenocarcinoma in cytologic preparations, 21 paraffin embedded cells blocks of serous effusions from 15 patients with metastatic adenocarcinoma and 16 cell blocks from 9 patients with malignant mesothelioma were stained with a monoclonal antibody against calretinin. The immunoreactivity was evaluated blindly by two observers. Positive staining was defined as nuclear and cytoplasmic staining with or without intense membranous decoration. The former resulted in a characteristic "fried egg" appearance.
  
  
  RESULTS
  Calretinin staining was positive in all but 2 cases of mesothelioma (14 of 16 cases; 87.5%). The latter contained predominantly spindle-shaped neoplastic mesothelial cells in the cell block preparations. All adenocarcinoma specimens were classified as negative for calretinin staining; 9 (42.9%) lacked any immunoreactivity and 12 (57.1%) showed weak, sparse, coarse, granular cytoplasmic staining without nuclear or membranous staining. Benign reactive mesothelial cells, when observed in association with adenocarcinoma, also showed the characteristic "fried egg" appearance. The difference in the staining pattern of calretinin between cells of mesothelial origin and adenocarcinoma cells was statistically significant.
  
  
  CONCLUSIONS
  Calretinin is a useful marker in differentiating mesothelioma of the epithelial type from adenocarcinoma in serous effusions. The "fried-egg" appearance or cytoplasmic and nuclear staining pattern is characteristic of cells of mesothelial origin.
authors.affiliation: Department of Pathology, New York University Medical Center, New York, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Chhieng
authors.forename: H
authors.initials: H
authors.lastname: Yee
authors.forename: D
authors.initials: D
authors.lastname: Schaefer
authors.forename: J F
authors.initials: JF
authors.lastname: Cangiarella
authors.forename: J
authors.initials: J
authors.lastname: Jagirdar
authors.forename: L A
authors.initials: LA
authors.lastname: Chiriboga
authors.forename: J
authors.initials: J
authors.lastname: Jagirdar
authors.forename: L A
authors.initials: LA
authors.lastname: Chiriboga
authors.forename: J M
authors.initials: JM
authors.lastname: Cohen
mesh_terms: D000230:Adenocarcinoma / Q000175:diagnosis*; D000911:Antibodies, Monoclonal; D001202:Ascitic Fluid / Q000737:chemistry; D014408:Biomarkers, Tumor / Q000032:analysis*; D064032:Calbindin 2; D002462:Cell Membrane / Q000648:ultrastructure; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008654:Mesothelioma / Q000175:diagnosis*; D010996:Pleural Effusion / Q000737:chemistry; D064030:S100 Calcium Binding Protein G / Q000032:analysis*; D012680:Sensitivity and Specificity
chemical_list: D000911:Antibodies, Monoclonal; D014408:Biomarkers, Tumor; C576764:CALB2 protein, human; D064032:Calbindin 2; D064030:S100 Calcium Binding Protein G