title: Assessment of HER2/Neu status by fluorescence in situ hybridization in immunohistochemistry-equivocal cases of invasive ductal carcinoma and aberrant signal patterns: a study at a tertiary cancer center.
abstract: BACKGROUND
  HER-2/neu status determines the eligibility for targeted therapy with trastuzumab in breast carcinoma. Evaluation for HER-2/neu protein expression by immunohistochemistry (IHC) and gene amplification by fluorescence in situ hybridization (FISH) has become the gold standard.
  
  
  OBJECTIVE
  Since data on HER-2/neu assessment by IHC and FISH and studies regarding concordance between the results of the two techniques are limited, especially from India, we sought to study HER-2 gene amplification status by FISH in equivocal (2+) cases by IHC and also study aberrant signal patterns.
  
  
  METHODS
  Mastectomies and breast core biopsies, equivocal for HER-2/neu protein expression, were analyzed for HER-2 amplification by FISH.
  
  
  METHODS
  IHC (DAKO) and FISH (PathVysion dual-probe system) tests were performed on 68 of 112 (after exclusion) 10% neutral buffered formalin (NBF)-fixed paraffin-embedded tissues and evaluated according to American Society of Clinical Oncology ASCO guidelines.
  
  
  METHODS
  Chi-square (χ2) test and the two-tailed P value were applied using Graphpad Quickcels software, version 2006.
  
  
  RESULTS
  It was found that 73.5% of the IHC 2+ patients were negative for HER-2/neu amplification, 25% were positive (ratios ranging from 2.3 to 5.6) and 1 patient was equivocal (2.2). Retesting FISH HER-2 equivocal case on another tumor block by IHC demonstrated HER-2 overexpression of protein 3+, thus resolving the equivocal status. Polysomy and HER-2 genetic heterogeneity were seen frequently.
  
  
  CONCLUSIONS
  The findings reiterate that IHC HER-2 equivocal cases are a heterogeneous group and need FISH for further categorization. Low concurrence (25%) rate between both IHC and FISH results in the equivocal scenario can be attributed to tumors with polysomy 17 and HER-2/neu genetic heterogeneity.
authors.affiliation: Department of Laboratory Medicine (Pathology and Molecular Diagnostics), Basavatarakam Indo-American Cancer Hospital and Research Institute, Hyderabad, India. sudha.s@induscancer.com
authors.forename: Sudha S
authors.initials: SS
authors.lastname: Murthy
authors.forename: D G
authors.initials: DG
authors.lastname: Sandhya
authors.forename: Faiq
authors.initials: F
authors.lastname: Ahmed
authors.forename: K Iravathy
authors.initials: KI
authors.lastname: Goud
authors.forename: Monal
authors.initials: M
authors.lastname: Dayal
authors.forename: K
authors.initials: K
authors.lastname: Suseela
authors.forename: Senthil J
authors.initials: SJ
authors.lastname: Rajappa
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D001940:Breast / Q000473:pathology; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000473:pathology; D044584:Carcinoma, Ductal / Q000175:diagnosis* / Q000473:pathology; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence / Q000379:methods*; D007194:India; D008408:Mastectomy; D008853:Microscopy; D008875:Middle Aged; D057089:Pathology, Molecular / Q000379:methods*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics*
chemical_list: D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human