HER2 status in gastric/gastro-oesophageal junctional cancers: Should determination of gene amplification by SISH use HER2 copy number or HER2:CEP17 ratio?

Abstract

The aim of this study was to compare HER2 amplification, as determined by the HER2 copy number (CN) and the HER2/CEP17 ratio, with protein expression in gastric and gastrooesophageal junction (G/GOJ) adenocarcinoma. HER2 immunohistochemistry (IHC) and silver in situ hybridisation (SISH) were performed in 185 cases. Modified gastric criteria were used for IHC scoring. HER2 and CEP17 CNs were counted in at least 20 cancer cells and the ratio calculated as per previously defined protocols. These two SISH methods were statistically compared against the different IHC scores. Thirty-four cases showed amplification, by both methods in 29, and either method in five. IHC score was 3+ in 29 cases; 26 ..