['\u2002 Epithelial-mesenchymal transition (EMT) is characterized by a loss of epithelial nature and the acquisition of a mesenchymal form. The aim of this study was to assess the role of EMT in human mammary carcinogenesis, by performing immunohistochemical studies of EMT markers with tissue microarrays.', '\u2002 A total of 492 cases were evaluated and classified as hormone receptor (HR)-positive type, HER2 type and triple-negative (TN) type by the use of immunohistochemistry and in-situ hybridization. We compared these groups in terms of epithelial and mesenchymal marker expression patterns. Of the 102 cases of TN-type breast cancer, 24.5% expressed vimentin, 13.7% expressed N-cadherin, and 9.8% expressed smooth muscle actin (SMA). Of the 221 cases of HR-type breast cancer, 4.1% expressed vimentin, 5.9% expressed N-cadherin, and 0.4% expressed SMA. Regarding epithelial markers, decreased expression was seen in 16.7% of cases for E-cadherin, in 45.1% for cytokeratin (CK)19 and in 60.8% for CK8 and CK18 (CAM5.2) in TN-type breast cancer cases. Decreased expression was seen in 11.8% of cases for E-cadherin, in 6.8% for CK19 and in 3.2% for CAM5.2 in HR-type cases.'] Does epithelial-mesenchymal transition in breast cancer correlate with high histological grade and triple-negative phenotype?