HER2 amplification in gastric cancer is a rare event restricted to the intestinal phenotype

The objectives of this study were to identify HER2 prevalence in gastric cancer and correlate it with location, phenotype, and follow-up. Consecutive gastric cancer patients with tissue blocks, gross data, and follow-up data, were submitted to immunohistochemistry (IHC) with HercepTest. Chromogenic and fluorescence in situ hybridization was performed in IHC-positive tumors. A total of 269 patients were included with a median age of 61 years. In 172 gastrectomized patients, histotypes were diffuse (72, 41.8%), intestinal (63, 36.6%), and mixed (37, 21.5%). HER2 IHC expression was 0 in 167, 2+ in 2, and 3+ in 3 tumors. Only endoscopic biopsies were available in 97 patients and HER2 IHC expression was 0 in 88, 1+ in 3, 2+ in 4, and 3+ in 2 patients. In all, 10/269 (3.7%) had HER2 amplification. Amplified tumors were intestinal adenocarcinomas located throughout the different regions of the stomach. Heterogeneity was documented in 4 widely sampled tumors. HER2 amplification was restricted to the intestinal phenotype. It is a rare event and its screening should be driven by gastric cancer histotype.