To demonstrate our hypothesis, we analyzed the expression of hypoxia inducible factor-1α (HIF-1α) and Foxp3 in gastric cancer tissues, assessed the effect of hypoxia on TGF-β1 production in cancer cell lines, and finally elucidated the role of hypoxia mediating Treg enrichment in gastric cancer. The gene discussed is TGFB1; the disease is gastric cancer.