Gastric adenocarcinoma SGC-7901 murine models that were subcutaneously injected and orally administered with COS-Se for 28 days exhibited significantly reduced tumor volumes and weights, reduced expressions of pro-angiogenesis related factors (e.g., CD34 and vascular endothelial growth factor (VEGF)) in the treated tumor tissues, and decreased serum levels of tumor metastasis-related targets (e.g., matrix metalloproteinase-9 (MMP-9) and VEGF) relative to the control group, demonstrating the anti-cancer efficacy of COS-Se in vivo. The gene discussed is VEGFA; the disease is gastric adenocarcinoma.