It has been found that significantly increased numbers of tumor-infiltrating Tregs are seen in lung metastasis models of colon cancer as well as an increased proportion of Tregs in cytokine-induced killer cells (CIKs), so in this study, we investigated the effects of As2O3 on the infiltration of Tregs in local lung metastasis of mouse colon cancer in vivo and the regulation of Tregs in CIKs in vitro. This evidence concerns the gene TRAF3IP2 and malignant colon neoplasm.