title: False positivity in HER2 testing of breast cancer: novel paths for approaching an old dilemma.
abstract: OBJECTIVE
  Variability in determining HER2 status has been reported, especially, differences in sensitivity and specificity among commercially available antibodies, with false positive and false negative results. We compared the sensitivity and specificity of five anti-HER2 antibodies by immunohistochemistry (IHC), using the new dual colour brightfield in situ hybridisation (DDISH) as the gold standard, on invasive breast carcinomas (IBC) arrays.
  
  
  METHODS
  Serial sections from tissue microarrays (TMA) containing 200 preselected primary IBC were submitted to DDISH (VENTANA INFORM HER2 Dual ISH assay), and immunohistochemistry, using Dako A0485 and HercepTest (polyclonal), Novocastra CB11 (mouse monoclonal), NeoMarkers SP3 and Ventana 4B5 (rabbit monoclonal).
  
  
  RESULTS
  From the initial 200 cases, 184 were assessed by DDISH and IHC. The concordance among the antibodies was considered very good (kappa statistics varied from 0.82 to 0.9). The overall concordance between IHC and DDISH ranged from 94.1% for CB11 to 96.6% for A0485. The antibodies A0485, HercepTest, SP3 and 4B5 were over 95% sensitive and specific. CB11 was the most specific antibody (97.1%). 60% (CB11) to 83.3% (SP3) of the 2+ cases showed no gene amplification by DDISH. False negative cases varied from 0.5% (A0485) to 3.8% (CB11) of the cases, and false positive from 1.6% (CB11) to 2.7% (HercepTest, SP3 and 4B5) of the 184 cases.
  
  
  CONCLUSIONS
  There was very good agreement among the five anti-HER2 antibodies. CB11 was the most specific antibody, but showed more false negative cases. A0485, SP3, 4B5 and HercepTest were highly sensitive and specific, but showed more false positive cases.
authors.affiliation: Department of Anatomic Pathology, Federal University of Minas Gerais, , Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Cristiana Buzelin
authors.initials: CB
authors.lastname: Nunes
authors.forename: Rafael Malagoli
authors.initials: RM
authors.lastname: Rocha
authors.forename: Marcelo Araújo
authors.initials: MA
authors.lastname: Buzelin
authors.forename: Débora
authors.initials: D
authors.lastname: Balabram
authors.forename: Fernanda
authors.initials: F
authors.lastname: de Souza Foureaux
authors.forename: Simone Souza
authors.initials: SS
authors.lastname: Porto
authors.forename: Helenice
authors.initials: H
authors.lastname: Gobbi
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D000912:Antibodies, Neoplasm / Q000276:immunology*; D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D001943:Breast Neoplasms / Q000473:pathology*; D005188:False Negative Reactions; D005189:False Positive Reactions; D005260:Female; D005784:Gene Amplification; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization / Q000379:methods*; D051379:Mice; D011817:Rabbits; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D012680:Sensitivity and Specificity; D046888:Tissue Array Analysis
chemical_list: D000911:Antibodies, Monoclonal; D000912:Antibodies, Neoplasm; D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor; D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human
keywords: Antibodies; Breast Cancer; Cerb 2; Immunohistochemistry