Metastasis is the main cause of death in cancer patients.To improve the outcomes of patients undergoing a surgery,new adjuvant therapies that can effectively inhibit metastases have to be developed.Studies have shown that flavonoid naringenin,a natural product that is mainly present in grapes and citrus,may contribute to cancer prevention.It has many advantages compared to traditional chemotherapeutic drugs,such as low toxicity.To determine whether naringenin can also inhibit metastases,a breast cancer resection model that mimics clinical situations was established.We found that orally administered naringenin significantly decreased the number of metastatic tumor cells in the lung and extended the life span of tumor resected mice.Flow cytometry analysis revealed that T cells displayed enhanced antitumor activity in naringenin treated mice,with an increased proportion of IFN-y and IL-2 expressing T cells.In vitro studies further demonstrated that relief of immunosuppression caused by regulatory T cells might be the fundamental mechanism of metastasis inhibition by naringenin.These results indicate that orally administered naringenin can inhibit the outgrowth of metastases after surgery via regulating host immunity.Thus,naringenin can be an ideal surgical adjuvant therapy for breast cancer patients.