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The purpose of the study was to compare two methods used to analyse HER-2 gene amplification
(fluorescence in situ hybridisation (FISH) and chromogenic in situ hybridisation (CISH)),
and determine the accuracy of the antibodies CB11 and HercepTest for immunohistochemical
detection of HER-2 overexpression from archival breast cancer tissue. Additionally,
interobserver variability in the interpretation of CISH and immunohistochemical tests
was measured. Two hundred cases of invasive breast carcinoma diagnosed between 2000
and 2003 were selected. Immunohistochemistry (IHC) was performed with HercepTest and
CB11, and gene amplification was determined by FISH (PathVision, Vysis) and CISH (Zymed)
using tissue macroarrays. An excellent concordance (94.8%) was found between CISH
and FISH. Considering FISH as gold standard, sensitivity of CISH was 97.5% and specificity
94%. Overall interobserver agreement of CISH was 97.5% and of IHC 84%. Both antibodies
showed a sensitivity of 95.2% and a specificity of 70.7% (CB11) and 81.2% (HercepTest).
Our results show that CISH is a highly accurate, reproducible and practical technique
to determine HER-2 gene amplification. CB11 and HercepTest are good screening methods
with a high sensitivity. The performance of tissue macroarrays to test HER-2 status
by IHC, FISH and CISH has demonstrated to be an available and effective method to
study large series of tumours.