title: Interobserver reproducibility for HER2/neu immunohistochemistry: A comparison of reproducibility for the HercepTest™ and the 4B5 antibody clone.
abstract: BACKGROUND
  IHC results for HER2/neu vary with replicate testing using the same antibody clone and when alternate clones are utilized. A number of factors appear to be responsible for this variability, including fixation times, equipment utilized and training and experience of staff. A number of studies have documented interobserver variability for a single antibody clone but few have evaluated reproducibility between antibody clones and which clones demonstrate the highest degree of interobserver reproducibility.
  
  
  METHODS
  We studied a series of 93 cases stained by both the HercepTest™ and the 4B5 clone for interobserver reproducibility. Formalin-fixed, paraffin-embedded sections were stained by the immunohistochemical technique using the manufactures directions for both the HercepTest™ and the 4B5 clone. FISH testing was performed on formalin-fixed paraffin embedded sections according to the PathVysion HER-2 DNA probe kit instructions.
  
  
  RESULTS
  Absolute agreement rate for Hercep was 85%. Absolute agreement for 4B5 was 69%. This difference was statistically significant (p<0.0001). The chance-corrected agreement (weighted kappa) for the HercepTest™ was 79% and 71% for 4B5 (p<0.0001). Absolute agreement between antibody clones was 58% with the chance corrected agreement being 51%. Absolute agreement of 4B5 with FISH was significantly greater than that of the HercepTest™ (54% vs 35%).
  
  
  CONCLUSIONS
  Agreement between evaluators was greater with the HercepTest. However, agreement with FISH results was superior for the 4B5 clone. Interobserver agreement was less than the 95% agreement threshold recommended by the ASCO/CAP guidelines for development of a new testing method for HER2 evaluation.
authors.affiliation: From the Department of Pathology & Anatomical Sciences, University of Missouri, Columbia, MO, United States. Electronic address: layfieldl@health.missouri.edu.
authors.forename: Lester J
authors.initials: LJ
authors.lastname: Layfield
authors.affiliation: From the Department of Pathology & Anatomical Sciences, University of Missouri, Columbia, MO, United States.
authors.forename: Shellaine
authors.initials: S
authors.lastname: Frazier
authors.affiliation: From the Department of Pathology & Anatomical Sciences, University of Missouri, Columbia, MO, United States.
authors.forename: Magda
authors.initials: M
authors.lastname: Esebua
authors.affiliation: From the Department of Pathology & Laboratory Medicine and ARUP Laboratories, Salt Lake City, UT, United States.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Schmidt
mesh_terms: D000911:Antibodies, Monoclonal; D014408:Biomarkers, Tumor / Q000032:analysis*; D001943:Breast Neoplasms / Q000175:diagnosis*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry / Q000592:standards*; D017404:In Situ Hybridization, Fluorescence / Q000379:methods; D015588:Observer Variation; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis*; D015203:Reproducibility of Results
chemical_list: D000911:Antibodies, Monoclonal; D014408:Biomarkers, Tumor; D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human
keywords: 4B5; Breast carcinoma; HER2; HercepTest™; Immunohistochemistry; Interobserver reproducibility