In contrast to pancreatic cancer stem cells in which CD133+/CXCR4− cells are just as tumorigenic as CD133+/CXCR4+ cells, in prostate tumor initiating cells CXCR4 expression results in significantly greater colony formation (Figure 2F) and inhibition of CXCR4 with an antagonistic antibody reduces tumor growth (Figure 6D). This evidence concerns the gene PROM1 and prostate neoplasm.