“…Cancer cell heterogeneity and hierarchy may be resulted from both genetic and/or epigenetic causes. Increasing evidence from hematopoietic malignancies and solid tumors (including brain, breast, colorectal, head and neck cancers) has strongly supported the concept that a subpopulation of cancer cells in each tumor has greater potential of cancer initiation and repopulation (Lapidot et al, 1994;Bonnet and Dick, 1997;Al-Hajj et al, 2003;Hemmati et al, 2003;Singh et al, 2003;Galli et al, 2004;Singh et al, 2004;Ricci-Vitiani et al, 2007;O'Brien et al, 2007;Dalerba et al, 2007;Prince et al, 2007;Schatton et al, 2008). These cells were called cancer stem cells (CSCs) or tumor-initiating or propagating cells because they share some critical characteristics with normal stem cells, including the capacities for self-renewal, multi-lineage differentiation, and maintained proliferation (Reya et al, 2001;Vescovi et al, 2006;Bao et al, 2006a;Rosen and Jordan, 2009;Park and rich, 2009;Heddleston et al, 2010;Frank et al, 2010).…”