CD44 and breast cancer: Importantly, the purified CD44+/CD24− cells (mesenchymal-like cancer stem cell state) are able to generate heterogeneous populations that recreate the proportion of CD44+/CD24− and aldehyde dehydrogenase (ALDH) expressing cells (epithelial-like cancer stem cell state) present in the original cell lines (including MCF-7) (14), indicating that cellular plasticity enables breast cancer stem cells to transit between different phenotypes.