Objective To investigate the effects of estrogen and tamoxifen on the expression of high mobility group box 1(HMGB1) in human breast cancer cell line MCF-7.Methods MCF-7 cells were incubated with 17-beta E2 and tamoxifen at different concentrations for 4 days,respectively,with ethanol as control.Real time RT-PCR and Western blotting were used to detect the expression of HMGB1 at mRNA and protein level after different treatment of the cell line,respectively.Results Compared with ethanol control,HMGB1 mRNA and protein level were significantly decreased when 17-beta-E2 was added at concentrations of 10-6 and 10-4 mol/L(P