Tamoxifen(TAM)has been one of the most widely applied endocrine drugs for the treatment of ER positive breast cancer.Unfortunately,clinical resistance to tamoxifen is frequent and precedes death from metastases.In our recent study,we found that Nrf2 showed higher expression in MCF-7 tamoxifen resistant cells(MCF-7/TR)than in MCF-7 parental cells(MCF-7/P),so as other anti-oxidant genes,such as SOD1,ME1,HO1,GPX2 and so on.All these higher expression genes led to reactive oxygen species(ROS)stayed in a lower level.We then demonstrated that higher expression of c-Myc was one of the mechanisms for Nrf2 activation.In previous reports,niclosamide showed effects of anti-tumours,our results suggested that niclosamide inhibits the expression of c-myc,and increases ROS levels to induce apoptosis in MCF-7/TR cells.Interestingly,TR cells showed more sensitivity when applied both niclosamides and 4-OH TAM,which implied that niclosamide might be used as a combination drug for the treatment of tamoxifen resistant breast cancer patients.