It should also be mentioned that the percentage of CD44+ and CD166+ cells, which are known to be colon cancer initiating cells and are resistant to chemotherapy [16], was not increased under hypoxia and serum free conditions, raising the issue of whether there are two different populations of TICs, i.e. CD133+ and CD44+/CD166+. This evidence concerns the gene PROM1 and malignant colon neoplasm.