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.