The objective of this study is to investigate the proportion of HER2 overexpression in gastric cancer patients group, to evaluate the relation of HER2 overexpression with prognosis, and to analyze the proportion of herceptin applied to patients in clinical field. Furthermore, the investigators are going to reevaluate the clinical benefit of Herceptin for survival prolongation compared to chemotherapy only.

Inclusion Criteria:

1. Histologically confirmed gastric adenocarcinoma
2. Patients were diagnosed during 2006-2013
3. HER2 expression status was evaluated in primary gastric cancer or metastatic lesion.

Exclusion Criteria:

• Patients with second primary cancer within 5 years

gastric cancer patients in Gangnam Severance Hospital