Year: 2010
Type: dissertation
Study design: Observational Study
Abstract: The HER2 gene is amplified in 20-30% of breast cancers, a common cancer amongst \nSouth African women. HER2 amplification is associated with a poor prognosis and \npredicts response to treatments such as Herceptin. The gold standard for HER2 testing \nis Fluorescent in situ Hybridisation (FISH) with dual colour probes for the HER2 \ngene and chromosome 17 centromere (CEP17) internal control. According to \ninternational guidelines, a HER2/CEP17 ratio >2.2 is considered positive. The HER2 \nFISH test is complicated by the emergence of ambiguous cases with increased CEP17 \nsignals that cannot be accounted for by chromosome 17 polysomy (> 6 copies of \nCEP17) and that may hide true HER2 gene amplification. \nThe aims of this study were to characterise the HER2 amplicon, in particular the copy \nnumber of genes in the vicinity of the HER2 gene, and to design an alternative control \nprobe that could clarify the HER2 gene status in ambiguous cases. In addition, results \non 1558 breast cancer specimens sent for routine testing were analysed to determine \nthe trends of HER2 amplification amongst South African women. \nThe rate of HER2 gene amplification was significantly higher (p < 0.05) in African \npatients (52%) than in Caucasian patients (43%). In Caucasian women, the rate of \nHER2 amplification in the younger group (68%) was significantly higher (p < 0.05) \nthan in the general Caucasian group (43%), while the same was not seen in the \nAfrican cohort. \nNineteen ambiguous cases with more than 9 copies of CEP17 were further \ninvestigated. FISH assays with four different probe kits (PathVysion HER-2: \nPoseidon Repeat free TOP2A, HER2, CEP17: and Vysis PML-RARA respectively) \nwere performed to determine the copy number of the HER2, TOP2A, RARA genes \nand CEP17. An in-house dual colour probe kit was designed using the ACTG1 gene \nas a control for HER2. Of the 19 ambiguous cases, 16 had centromeric amplification, \nshowing that CEP17 is no longer an adequate internal control in FISH HER2 testing. \nThe TOP2A gene was only amplified in HER2 positive cases and the RARA gene \nwas only amplified when the TOP2A gene was also amplified. FISH with ACTG1 as \nv \na control clearly revealed HER2 amplification in ambiguous cases on image analysis \nand gave HER2/ACTG1 ratios significantly higher than HER2/CEP17 ratios. \nHowever, screening of an additional 40 unambiguous cases showed an increased copy \nnumber, although limited ( 8), of the ACTG1 gene in four patients; this warrants \nfurther testing to assess the value of this gene as a control. Interestingly, a trend was \nobserved for ACTG1 increased copy number in HER2 negative cases, this may point \nto the presence of a driver gene whose amplification tends to be mutually exclusive from HER2 amplification.
Author: Olivia Herd
Language: English
Topic: HER2/EGFR in Cancer Research
Subfield: Oncology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2162461238