Abstract: Objective To detect the level of Twist gene in circulating tumor cells(CTCs)in patients with metastatic breast cancer and evaluate the reaction to treatment of every patient.We tried to discuss the prediction significance of Twist in CTCs to curative effect.Methods We detected the expression of Twist gene in CTCs from 58 metastatic breast cancer(MBC)patients by magnetic activated cell sorting(MACS)technology combined with RT-PCR.We evaluated the clinic significance and the curative effect of chemotherapy in MBC patients using Response Evaluation Criteria in Solid Tumors(RECIST).Results There was no positive expression of Twist mRNA in blood samples from 10 healthy volunteers based on our methods.Among 58 MBC samples, 19/58(32.8%)were found to express Twist mRNA.In three different breast cancer subgroups, Twist mRNA was expressed more frequently in the triple negative subgroups than in luminal A and Her-2 positive subgroups(P＜0.001).After two cycles of chemotherapy, the overall response rate(ORR)of MBC patients to chemotherapy in Twist mRNA positive group was lower than in Twist mRNA negative group(P＜0.05).Conclusion Some CTCs undergo EMT and express epithelial mesenchymal transition gene Twist.CTCs undergoing EMT in breast cancer patients may have a survival advantage because of resistance to chemotherapy.The presence of mesenchymal CTCs predicted resistance to chemotherapy and they maybe one of the reasons of invalid therapy of triple negative breast cancer.