Following the standard biomarkers of breast cancer stem cells (BCSCs) (4) and our established BCSCs from MCF7/C6 with HER2 induction as radiation-derived BCSCs (RD-BCSCs; CD44+/CD24−/low/HER2+ with enhanced ALDH activity (8), we compared the tumorspheres from RD-BCSCs and MCF7 shown in Figure 2A. Here, CD44 is linked to breast cancer.