Similar to the isolation and characterization of CD133+ cells, SP cells from a variety of sarcomas have been isolated by FACS and shown to be capable of initiating tumor formation in immunodeficient mice as well as self-renewal properties as evidenced by serial transplantation experiments (Wu et al., 2007; Tirino et al., 2008; Murase et al., 2009). The gene discussed is PROM1; the disease is sarcoma.