Objective To investigate the effects and mechanism of TET2 inhibitor itaconate in prolifer-ation and migration of breast cancer cell line MDA-MB-231.Methods The MDA-MB-231 cells were treated for 24 h with dimethyl sulfoxide(DMSO)and 1,5 μmol/L itaconate respectively.The cellular apoptosis was determined by flow cytometry to determine the available itaconic acid concentration.The immunofluorescence was performed to determine the inhibiting effect of itaconate on hydroxymethylcytosine(5hmC)expression level.The cell counting and MTS were performed to determine the effect of itaconate on cell proliferation and activity.The Transwell experiment was performed to determine the effect of itaconate on cell transfer ability.The methylation-specific real-time fluorescence quantitative PCR(qPCR)was used to detect the effects of ita-conic acid treatment on the methylation of promoter regions of genes related to cell proliferation and migra-tion.qPCR was used to detect the effects of itaconate on the cellular proliferation,migration related genes ex-pression.Results 5 μmol/L itaconate treating the cells had no significant effect on the cellular apoptosis,mo-reover could inhibit 5hmC expression level.The cell count and MTS results showed that itaconate could pro-mote the cell proliferation(increase by about 58％,P＜0.05)and increase the cell activity(increase by 42％,P＜0.05).The Transwell experiment results showed that itaconate increased the cell migration(increase by 55％,P＜0.05).The methylation-specific qPCR showed that the itaconate treatment significantly promoted the methyaltion of the promoters p21 and PTEN.The qPCR results showed that itaconate significantly inhibi-ted the expression levels of p21 and PTEN(P＜0.05).Conclusion Itaconate promotes the proliferation and migration of MDA-MB-231 cells through inhibiting 5hmC level of p21 and PTEN and decrease its expression.