title: Determination of HER2 amplification by in situ hybridization: when should chromosome 17 also be determined?
abstract: Our purpose was to determine the accuracy of diagnosis of HER2 amplification by analysis of HER2 copy number. HER2 and chromosome 17 were measured by dual-color fluorescence in situ hybridization in breast cancer samples. At a HER2 copy number of 2 to less than 3, 16 (3.3%) of 488 cases had HER2 amplification; and at a copy number of 3 to less than 4, 32 (16.4%) of 195 cases were amplified. The proportion of cases with HER2 amplification increased considerably at HER2 copy numbers of 4 to less than 7: 50.0% at 4 to less than 5; 67.5% at 5 to less than 6, and 77.3% at 6 to less than 7. Virtually all cases were amplified at HER2 copy numbers of 7 or more. We recommend that all breast cancer cases with a HER2 copy number of 2 to 7 determined by single-color in situ hybridization should also be analyzed for chromosome 17 to obtain a more accurate diagnosis of HER2 amplification.
authors.affiliation: Endocrine Cancer Group, Edinburgh University Cancer Research Centre, Western General Hospital, Edinburgh, Scotland, UK.
authors.forename: John M S
authors.initials: JM
authors.lastname: Bartlett
authors.forename: Fiona M
authors.initials: FM
authors.lastname: Campbell
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Mallon
mesh_terms: D000782:Aneuploidy; D001943:Breast Neoplasms / Q000235:genetics / Q000473:pathology*; D002886:Chromosomes, Human, Pair 17 / Q000235:genetics*; D003951:Diagnostic Errors / Q000517:prevention & control; D005784:Gene Amplification; D018734:Genes, erbB-2 / Q000235:genetics*; D006801:Humans; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence / Q000379:methods*