In contrast, breast cancers with a basal-like phenotype [3] are characterized by a protein expression pattern which is similar to that of myoepithelial cells, including a higher expression of high molecular weight cytokeratins, such as CK5, CK14 and CK17, smooth muscle markers, p63, CD10, EGFR/HER1, or beta-4 integrin, among others, and a lower expression of ER, PR, or HER2. This evidence concerns the gene ESR1 and breast cancer.