To test our hypothesis that only a small subpopulation of highly proliferative ARO cells is responsible for tumor formation, we transplanted groups of NOD/SCID mice with increasing numbers of CD133+/high, CD133+/low and CD133− cells - from an amount normally unable to initiate tumor growth (∼1,000 cells) to an amount that always initiates tumor growth (∼100,000 cells). This evidence concerns the gene PROM1 and neoplasm.