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

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 gastro-oesophageal 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.