CD44 and breast cancer: Recently, CSCs have been isolated from several human solid tumours that have markers for putative normal stem cells, including breast cancer (CD44+CD24−ESA+) (Al-Hajj et al, 2003), pancreatic cancer (CD44+CD24−ESA+, CD133+CXCR4+) (Hermann et al, 2007; Li et al, 2007), brain cancer (CD133+) (Singh et al, 2004), prostate cancer (CD44+/α2β1hi/CD133+) (Collins et al, 2005), hepatocellular carcinoma (CD133+) (Yin et al, 2007) and colon cancer (CD133+) (Ricci-Vitiani et al, 2007).