title: Determination of HER2 gene amplification by fluorescence in situ hybridization and concordance with the clinical trials immunohistochemical assay in women with metastatic breast cancer evaluated for treatment with trastuzumab.
abstract: OBJECTIVE
  To evaluate the concordance between HER2 gene amplification, determined by fluorescence in situ hybridization (FISH), and HER2 protein overexpression assessed by an immunohistochemical (IHC) assay. The IHC protocol used was a research assay, known as the Clinical Trial Assay (CTA), developed to select women with metastatic breast cancer (MBC) for three pivotal clinical trials of trastuzumab therapy.
  
  
  METHODS
  A direct-labeled, dual-probe FISH assay was used to determine HER2 amplification in 623 fixed breast cancer tissue specimens. These specimens had been stored as paraffin-embedded sections for 25 years. All specimens had been analyzed for HER2 protein expression by the CTA. To assess the reproducibility of FISH results in archived material, we evaluated a separate group of 617 breast cancer tissue specimens at two different laboratories.
  
  
  RESULTS
  Informative FISH results were available for 529 (85%) of the 623 specimens. Overall concordance between FISH and IHC results was 82% (95% CI; 7885%). Assay agreement between FISH results and specimens with immunostaining scores of 0, 1+, and 3+ were 97, 93 and 89%, respectively. However, only 24% of specimens with 2+ immunostaining scores had HER2 amplification by FISH; there was assay disagreement in 76% of specimens in this IHC subgroup. Interlaboratory FISH concordance was 92% (95% CI; 8994%), indicating very good assay reproducibility in these archived specimens.
  
  
  CONCLUSIONS
  HER2 status determined by CTA-IHC and FISH are significantly correlated; however, differences between these two assays can a ect patient selection for trastuzumab therapy.
authors.affiliation: Genentech Inc., South San Francisco, CA 94080, USA. nod@gene.com
authors.forename: Noël
authors.initials: N
authors.lastname: Dybdal
authors.forename: Grazyna
authors.initials: G
authors.lastname: Leiberman
authors.forename: Steven
authors.initials: S
authors.lastname: Anderson
authors.forename: Bryan
authors.initials: B
authors.lastname: McCune
authors.forename: Alex
authors.initials: A
authors.lastname: Bajamonde
authors.forename: Robert L
authors.initials: RL
authors.lastname: Cohen
authors.forename: Robert D
authors.initials: RD
authors.lastname: Mass
authors.forename: Corsee
authors.initials: C
authors.lastname: Sanders
authors.forename: Michael F
authors.initials: MF
authors.lastname: Press
mesh_terms: D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002986:Clinical Trials as Topic; D005260:Female; D005784:Gene Amplification; D015972:Gene Expression Regulation, Neoplastic; D018734:Genes, erbB-2 / Q000235:genetics*; D006801:Humans; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence; D009362:Neoplasm Metastasis; D016612:Paraffin Embedding; D011237:Predictive Value of Tests; D000068878:Trastuzumab
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D000068878:Trastuzumab