CD24 and breast cancer: Breast cancer cells in tumor tissues exhibit luminal, basal, and BCSCs phenotypes based on the expression of epithelial cell adhesion molecule (EpCAM), CD49f (α6 integrin), CD44, and CD24; EpCAM+/CD49f- mature luminal cells, EpCAM+/CD49f + luminal progenitors, EpCAM-/CD49f + basal progenitors [9, 10], BCSCs with EpCAM low/-/CD44+/CD24- marker and high activity of aldehyde dehydrogenase 1 (ALDH1) [6, 7].