Objective      To investigate the changes of the cell morphology and the expression of epithelial-mesenchymal transition (EMT) marker proteins after MCF-7 cells acquired tamoxifen resistance.       Methods      The cell morphology was revealed through immunofluorescent staining. The expression of EMT marker proteins was detected by quantitative real-time PCR (qRT-PCR) and Western blotting. Transwell assay was used to detect the difference of cell migration. PI3K-Akt and MAPK/Erk signaling pathways were evaluated in MCF-7 cells and tamoxifen-resistant MCF-7R cells. The migration and the expression of EMT marker proteins were reevaluated after inhibiting the signaling pathways.       Results      In the MCF-7 cells

intercellular contact was close and E-cadherin was predominantly localized in the membrane. However

cell contact became loose and E-cadherin was almost translocated to the cytoplasm in the tamoxifen-resistant MCF-7R cells. The migration was enhanced and the expression of vimentin and fibronectin was increased when the MCF-7 cells acquired tamoxifen resistance (P0.05). PI3K-Akt and MAPK/Erk signaling pathways were abnormally activated in the tamoxifen-resistant MCF-7R cells. Meanwhile

the migration and the expression of mesenchymal marker proteins were significantly suppressed when inhibiting PI3K-Akt pathway rather than MAPK/Erk pathway (P0.05).       Conclusion      EMT may contribute to the increased migration of tamoxifen-resistant breast cancer cells.