ESR1 and breast cancer: Also, MCT1 and CD147, alone or in co-expression, were also associated with estrogen receptor (ER) and progesterone receptor (PR) absence, high histological grade and proliferative index (Ki67), and presence of basal markers such as cytokeratin 5, 14 and vimentin [23], supporting the role of MCT1/CD147 in breast cancer aggressiveness as well as in the maintenance of the glycolytic phenotype.