CD44 and breast cancer: Subsequent studies in solid tumours revealed that CD44+/CD24− and CD133+ sub-populations contained CSC populations in breast cancer and glioblastoma, respectively (Al-Hajj et al, 2003; Singh et al, 2004) whereas more recent evidence of their existence has been demonstrated in melanoma (Fang et al, 2005; Schatton et al, 2008), prostate (Patrawala et al, 2006), pancreatic (Li et al, 2007), and colon cancer (O’Brien et al, 2007; Ricci-Vitiani et al, 2007).