title: Comparison of HER2 Dual-Color and Fluorescence In Situ Hybridization in Breast Cancer:  A Cohort Study Emphasizing Equivocal Cases.
abstract: OBJECTIVE
  Human epidermal growth factor receptor 2 (HER2; ERBB2 gene) is of prognostic and predictive significance in breast carcinoma. Both fluorescence in situ hybridization (FISH) and dual-color in situ hybridization (DISH) methods are available. DISH and FISH are highly concordant in validation studies, but differences may be more prevalent in the equivocal range. Our goal was to compare FISH and DISH on a cohort enriched for equivocal cases, with respect to HER2 determination.
  
  
  METHODS
  The cohort was enriched for equivocal (2+) cases. DISH and FISH were evaluated using standard protocols and the results compared with respect to HER2 status, HER2 copy number, and HER2/chromosome 17 (Chr17) ratio.
  
  
  RESULTS
  In total, 109 cases were identified. The agreement rate of DISH with FISH was 74%. The mean ± SD HER2/Chr17 ratio by DISH was 1.63 ± 0.08 vs 1.59 ± 0.26 by FISH (P = .45). The mean ± SD HER2 copy number by DISH was 4.56 ± 0.45 vs 4.75 ± 1.08 by FISH (P = .004). Individual signals were more easily resolved using FISH in cases with higher copy numbers.
  
  
  CONCLUSIONS
  In our cohort enriched for equivocal cases, the numerical values of HER2 copy number were significantly lower using DISH, resulting in discordances. Although DISH is a valid method, variations with FISH may be expected in high-equivocal cases and in quality assurance activities.
authors.affiliation: From the Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada.
authors.forename: Tiffany
authors.initials: T
authors.lastname: Shao
authors.affiliation: Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada.
authors.forename: Martha
authors.initials: M
authors.lastname: Wood
authors.affiliation: Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada.
authors.forename: Anthony
authors.initials: A
authors.lastname: Wing
authors.affiliation: Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada.
authors.forename: Marta
authors.initials: M
authors.lastname: Hnatovska
authors.affiliation: Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada.
authors.forename: Maria
authors.initials: M
authors.lastname: Mendes
authors.affiliation: From the Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Brendan Mullen
authors.affiliation: From the Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Canada. mchang2@mtsinai.on.ca.
authors.forename: Martin C
authors.initials: MC
authors.lastname: Chang
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000235:genetics / Q000473:pathology; D015331:Cohort Studies; D005260:Female; D005784:Gene Amplification; D006801:Humans; D017403:In Situ Hybridization / Q000379:methods*; D017404:In Situ Hybridization, Fluorescence / Q000379:methods; D008875:Middle Aged; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics*
chemical_list: D018719:Erb-b2 Receptor Tyrosine Kinases; C508053:ERBB2 protein, human
keywords: Breast cancer; DISH; FISH; HER2; In situ hybridization