title: Relationship between pathological features, HER2 protein expression and HER2 and CEP17 copy number in breast cancer: biological and methodological considerations.
abstract: OBJECTIVE
  A few reports have assessed HER2 status in breast cancer by both dual-probe fluorescence in situ hybridisation (FISH) and immunohistochemistry (IHC) in an unselected and consecutive fashion, but CEP17 and HER2 copy number were not evaluated separately in these studies. Therefore, the aim of this study was to perform FISH testing for HER2 in a large number of breast tumours, irrespective of the IHC scores, which were also determined in all cases.
  
  
  METHODS
  Both FISH and IHC were applied to 200 tumours from 196 consecutive patients who underwent resection of primary breast cancer with the sentinel procedure and/or axillary dissection. Not only the ratio, but also mean HER2 and CEP17 copy number were determined and used in statistical analyses to evaluate relationships between FISH, IHC and clinicopathological features.
  
  
  RESULTS
  The amplification status based solely on HER2 signals was 98% concordant with results of dual-probe FISH. In non-amplified tumours, the mean CEP17 and HER2 copy number correlated, possibly because of cell cycling. Amplified tumours were histopathologically more aggressive than non-amplified tumours, and features of aggressiveness increased with the mean HER2 copy number. In both amplified and non-amplified tumours, a gene dosage effect was observed: an increase in the mean HER2 copy number was associated with a higher IHC score.
  
  
  CONCLUSIONS
  This working method and analysis enabled new insights to be obtained into the pathobiology of HER2 in breast cancer. The findings may be helpful in optimising the methodology of HER2 testing.
authors.affiliation: Department of Pathology, University Hospital, Ghent University, De Pintelaan 185, Ghent, Belgium.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Lambein
authors.forename: Marleen
authors.initials: M
authors.lastname: Praet
authors.forename: Ramses
authors.initials: R
authors.lastname: Forsyth
authors.forename: Rudy
authors.initials: R
authors.lastname: Van den Broecke
authors.forename: Geert
authors.initials: G
authors.lastname: Braems
authors.forename: Bart
authors.initials: B
authors.lastname: Matthys
authors.forename: Veronique
authors.initials: V
authors.lastname: Cocquyt
authors.forename: Hannelore
authors.initials: H
authors.lastname: Denys
authors.forename: Patrick
authors.initials: P
authors.lastname: Pauwels
authors.forename: Louis
authors.initials: L
authors.lastname: Libbrecht
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002886:Chromosomes, Human, Pair 17 / Q000235:genetics; D005260:Female; D018628:Gene Dosage; D052138:Genes, Neoplasm; D018734:Genes, erbB-2; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008207:Lymphatic Metastasis; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000378:metabolism; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism
chemical_list: D009363:Neoplasm Proteins; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; C508053:ERBB2 protein, human