For example, the CD44+α2β1+CD133+ cells purified from human prostate tumor samples (Collins et al., 2005), the CD44+ cells in several prostate cancer xenografts (Patrawala et al., 2006), and the BCRP+ putative PCSCs (Huss et al., 2005) are all AR-. This evidence concerns the gene PROM1 and prostate carcinoma.