title: Confirmation of a low HER2 positivity rate of breast carcinomas - limitations of immunohistochemistry and in situ hybridization.
abstract: BACKGROUND
  Accurate assessment of the human epidermal growth factor receptor 2 (HER2) of invasive breast cancer is essential to treatment decisions since the advent of targeted therapy with the humanized monoclonal antibody trastuzumab and the dual tyrosine kinase inhibitor lapatinib. In the literature, the percentage of HER2-overexpressed/amplified breast carcinomas range from 3% to 30%. The routinely assigned low rate of 9% of HER2-overexpressed breast carcinomas alarmed one of our gynecologists who requested to confirm our HER2 test results.
  
  
  METHODS
  A small study of 83 patients with breast carcinoma was designed to reexamine the routinely assessed HER2 status using immunohistochemistry and fluorescence in situ hybridization.
  
  
  RESULTS
  The low rate of 9% of HER2-overexpressed/amplified breast tumors (DIN1C-3, invasive carcinoma) could be confirmed. However, FISH revealed two false positive cases and one false negative case. Moreover a case with an equivocal result in FISH was detected.
  
  
  CONCLUSIONS
  The HER2 positivity rate may be as low as 9%. The novel ASCO/CAP criteria for assessing immunohistochemical results in HER 2 testing reduce the false positive rate of HER2. First-line testing with immunohistochemistry may obscure false positive and false negative test results. In heterogeneous carcinomas even fluorescence in situ hybridization may not succeed in a correct evaluation of HER2.
authors.affiliation: Institute of Pathology, University Hospital, Eberhard-Karls-University, Liebermeisterstrasse 8, 72076 Tuebingen, Germany. ulrich.vogel@med.uni-tuebingen.de
authors.forename: Ulrich F
authors.initials: UF
authors.lastname: Vogel
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis* / Q000235:genetics; D001707:Biopsy, Needle; D001943:Breast Neoplasms / Q000737:chemistry / Q000175:diagnosis* / Q000235:genetics / Q000473:pathology; D002277:Carcinoma / Q000737:chemistry / Q000175:diagnosis* / Q000235:genetics / Q000473:pathology; D005188:False Negative Reactions; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D007150:Immunohistochemistry / Q000592:standards; D017404:In Situ Hybridization, Fluorescence / Q000592:standards; D009361:Neoplasm Invasiveness; D016612:Paraffin Embedding; D011237:Predictive Value of Tests; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis* / Q000235:genetics; D015203:Reproducibility of Results; D046888:Tissue Array Analysis
chemical_list: D014408:Biomarkers, Tumor; D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human