Importantly, experimental evidence has demonstrated that although in breast cancer both the ALDH+ and CD44+/CD24− sub-populations have strong self-renewal capability and will regenerate tumor mass when they were implanted in mice, multiple research groups showed that ALDH+ and CD44+/CD24− populations are not identical in terms of their oncogenic characteristics and cells co-expressing ALDH+ and CD44+/CD24− may harbor most strongest oncogenic and self-renewal capability22–24. This evidence concerns the gene CD44 and breast cancer.