CXCR4 and malignant colon neoplasm: CXCR4, a chemokine receptor, is expressed both in normal tissue stem cells of the breast, lung, and prostate gland, as well as tumors formed in those organs [29–32] Consistent with a role of colon TIC’s, colon cancer micrometastases require CXCR4 to initiate proliferation, and CXCR4/CD133 dual positive cells demonstrate enhanced tumorigenic capabilities over unsorted cells [33, 34].