title: A novel gene-protein assay for evaluating HER2 status in gastric cancer: simultaneous analyses of HER2 protein overexpression and gene amplification reveal intratumoral heterogeneity.
abstract: BACKGROUND
  Human epidermal growth factor receptor 2 (HER2) protein overexpression and gene amplification are important biomarkers for trastuzumab treatment in breast and gastric cancer patients. Gastric cancer presents high rates of tumor heterogeneity, which may influence the results of HER2 testing. A novel gene-protein assay (GPA) can allow the simultaneous analysis of HER2 protein and gene status on a single slide.
  
  
  METHODS
  Using the tissue microarray technique, the HER2 status of each of 875 gastric cancer cases was evaluated by immunohistochemistry (IHC), brightfield dual-color in situ hybridization (DISH), and GPA. Intratumoral phenotypic and genotypic heterogeneity were evaluated by comparing the HER2 statuses of two tissue cores from each case.
  
  
  RESULTS
  There was excellent concordance between GPA and IHC (99.2 %), as well as between GPA and DISH results (99.3 %). HER2 positivity obtained by GPA was almost identical (99.8 %) to the results obtained by IHC and DISH assays. Intratumoral phenotypic heterogeneity was more frequently observed in IHC 2+ cases (63.5 %) compared with IHC 3+ cases (28.3 %). Phenotypic heterogeneity (48.8 %) was more frequently observed than genotypic heterogeneity (26.8 %). Tumor heterogeneity was consistently observed from early to advanced stages.
  
  
  CONCLUSIONS
  HER2-positive gastric cancers presented different levels of HER2 protein expression and gene amplification statuses within the same lesion in almost half the cases examined. Evaluating both phenotypic and genotypic heterogeneity may contribute to a deeper understanding and improved prediction of clinical outcome in gastric cancer patients treated with trastuzumab. This newly established GPA technology may also be useful for developing biomarkers for other molecularly targeted therapies.
authors.affiliation: Pathology Division, National Cancer Center Hospital East, 6-5-1 Kashiwanoha, Kashiwa, Chiba, 277-8577, Japan.
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Nishida
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kuwata
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Nitta
authors.forename: Eslie
authors.initials: E
authors.lastname: Dennis
authors.forename: Masaki
authors.initials: M
authors.lastname: Aizawa
authors.forename: Takahiro
authors.initials: T
authors.lastname: Kinoshita
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ohtsu
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ochiai
mesh_terms: D014408:Biomarkers, Tumor / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence / Q000379:methods; D025202:Molecular Diagnostic Techniques / Q000379:methods*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis / Q000235:genetics* / Q000378:metabolism*; D013274:Stomach Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D046888:Tissue Array Analysis
chemical_list: D014408:Biomarkers, Tumor; D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human