title: Claudin-4 immunohistochemistry is highly effective in distinguishing adenocarcinoma from malignant mesothelioma in effusion cytology.
abstract: BACKGROUND
  Adenocarcinoma can be challenging to distinguish from malignant mesothelioma in effusions, and this distinction often requires ancillary studies and clinical correlation. Immunohistochemistry for claudin-4, a tight-junction-associated protein, has recently been shown to distinguish adenocarcinoma from malignant mesothelioma, mostly in surgical specimens. Our aim was to validate and assess the immunoreactivity profile of claudin-4 in a large series of malignant effusions.
  
  
  METHODS
  We evaluated 159 malignant effusions (84 adenocarcinomas and 75 malignant mesotheliomas). Claudin-4 immunohistochemistry was performed on cell-block paraffin sections and scored for staining intensity, staining pattern (cytoplasmic versus membranous), and percentage of positive tumor cells. Appropriate positive and negative controls were used throughout.
  
  
  RESULTS
  All cases of mesothelioma were negative for claudin-4 (0 of 64). Eighty-three of 84 cases of adenocarcinoma were positive (99%); 1 case of serous carcinoma was negative. Most adenocarcinomas showed strong and diffuse membranous staining (71 of 84; 84%); 12 cases (14%) showed membranous staining of moderate intensity. The overall sensitivity for adenocarcinoma was 99% (83 of 84).
  
  
  CONCLUSIONS
  Claudin-4 immunohistochemistry effectively distinguishes adenocarcinoma from malignant mesothelioma with high sensitivity and specificity in the evaluation of malignant effusions.
authors.affiliation: Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.
authors.forename: Vickie Y
authors.initials: VY
authors.lastname: Jo
authors.forename: Edmund S
authors.initials: ES
authors.lastname: Cibas
authors.forename: Geraldine S
authors.initials: GS
authors.lastname: Pinkus
mesh_terms: D000230:Adenocarcinoma / Q000737:chemistry / Q000473:pathology*; D000368:Aged; D014408:Biomarkers, Tumor / Q000032:analysis*; D001707:Biopsy, Needle; D062506:Claudin-4 / Q000032:analysis*; D003581:Cytodiagnosis / Q000379:methods; D016208:Databases, Factual; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008654:Mesothelioma / Q000737:chemistry / Q000473:pathology*; D008875:Middle Aged; D016066:Pleural Effusion, Malignant / Q000737:chemistry / Q000473:pathology*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity
chemical_list: D014408:Biomarkers, Tumor; D062506:Claudin-4
keywords: adenocarcinoma; claudin-4; cytology; effusion; mesothelioma