Supplementary Material for: Clinicopathological Features and Prognostic Significance of HER2 Expression in Gastric Cancer

<b><i>Background:</i></b> HER2 positivity is reported to be &lt;20% in gastric cancer. Clinicopathological characteristics will be helpful to understand the biological features of HER2-positive gastric cancer. <b><i>Methods:</i></b> A total of 813 gastric cancer patients who underwent HER2 testing between January 2005 and December 2010 were included in this study. <b><i>Results:</i></b> Ninety-five (11.7%) patients had HER2-positive gastric cancer. Elevated serum carcinoembryonic antigen (CEA) concentration [odds ratio (OR), 5.629; p &lt; 0.001] and differentiated histology (OR, 3.717; p = 0.002) were significant predictive factors for HER2 positivity in localized disease. For recurrent or metastatic disease, elevated serum CEA concentration (OR, 2.545; p &lt; 0.001), differentiated histology (OR, 3.299; p &lt; 0.001), pulmonary metastasis (OR, 3.321; p = 0.001), and distant lymph node metastasis (OR, 2.286; p = 0.002) were significant predictive factors. Median disease-free survival (DFS) was shorter in HER2-positive patients than in others, especially in stage I or II disease (24.7 vs. 49.2 months; p &lt; 0.001). Among HER2-negative patients with stage II diseases, patients who received adjuvant chemotherapy had longer DFS than others (42.2 vs. 30.7 months; p = 0.025). <b><i>Conclusions:</i></b> Clinicopathological factors may be useful in predicting the HER2 positivity of gastric cancer. Further studies are needed to understand the molecular basis of HER2-positive gastric cancer.