BACKGROUND: HER2 status is a predictive biomarker of response to trastuzumab in 
advanced gastric or gastroesophageal junction (GEJ) adenocarcinoma. However, 
there is relatively little known about the role of HER2 in resected gastric or 
GEJ adenocarcinoma in the Western population.
METHODS: Retrospective, observational, single centre study of patients with 
gastric or GEJ adenocarcinoma undergoing surgery with curative intent between 
January 2007 and June 2014 in the University Hospital Complex of Santiago de 
Compostela. The expression of HER2 was determined by immunohistochemistry (IHC) 
using DAKO-HercepTest™ and gene amplification with DuoCISH using a DAKO-DuoCISH 
kit. The study of HER2 expression and amplification was carried out in all the 
patients and it was correlated with classic clinicopathological parameters, 
survival and recurrence pattern.
RESULTS: 106 patients were included. HER2 expression was as follows: 71.7% HER2 
negative, 21.7% HER2 equivocal and 6.6% HER2 positive, or with HER2 
overexpression. 13.2% of patients (14/106) had HER2 amplification by DuoCISH. A 
significant association was seen between overexpression and amplification of 
HER2 (p < 0.001).HER2 positivity was associated with the intestinal subtype (p = 
0.010) and a low grade of differentiation (p = 0.018). Likewise, HER2 was 
significantly associated with a worse prognosis: overall survival (OS) 32.3 
months HER2 positive versus 93.9 months HER2 negative (HR 0.42; confidence 
interval 95% 0.18-0.93; p = 0.028); and the presence of distant metastasis 
without accompanying locoregional recurrence (p = 0.048).
CONCLUSION: HER2 status defines a subgroup with differentiated 
clinicopathological characteristics, worse prognosis and distant dissemination, 
without accompanying locoregional recurrence, in patients with resected gastric 
or GEJ adenocarcinoma operated on in a Western population.