ObjectiveEpithelial to mesenchymal transition (EMT) was the initial process of invasion and metastasis leading to a relapse of breast cancer following resection and chemo-radiotherapy. Membrane type-1 Matrix Metalloproteinase (MT1-MMP) was confirmed to play an important role in EMT in various cancers. However, the MT1-MMP effects on EMT in breast cancer had not yet been studied. Here,We investigated the MT1-MMP effects on breast cancer EMTonset, invasion, and migration abilities in MCF-7 cells. MethodsExpressions of MT1-MMP and EMT-associated proteins including E-cadherin, N-cadherin, and Vimentin were detected by immunohistochemistry in 71 breast cancer resection samples. The relationships of MT1-MMP with clinic- pathological parameters were statistically analyzed, as well as EMT-associated proteins. Western blot tests were performed to test MT1-MMP and EMT-associated proteins expression levels in MCF-7 cells transfected by MT1-MMP plasmid. Wound-healing and transwell experiments were used to estimate MT1-MMP-induced invasion and migration. ResultsOverexpression of MT1-MMP was verified in 71 breast cancer patients. MT1-MMP levels were observed to be correlated with the breast cancer clinical TNM stage, lymph node metastasis, and tumor size. The EMT-associated proteins including N-cadherin and Vimentin expression levels were higher both in MT1-MMP strong positive breast cancer resection samples and MCF-7 cells transfected with MT1-MMP plasmid. Furthermore, MCF-7 cells also acquired more ability to migrate and invade according to the results of the wound-healing assays and transwell experiments.ConclusionMT1-MMP was overexpressed in breast cancer tissue, and MT1-MMP promoted breast cancer EMT incidence, which was closely associated with breast cancer invasion and migration.