Accordingly, the co-expression of well-known basal-like molecular features, including expression of the anti-apoptotic protein survivin, the dynamic emergence of the CD44+CD24−/low breast cancer stem cell (CSC) immunophenotype, or the occurrence of epithelial-to-mesenchymal transition (EMT) phenomena, occurs exclusively in HER2+ breast cancer cells exhibiting primary resistance to trastuzumab [10, 19, 24–30]. Here, CD44 is linked to breast cancer.