Although both isolation methods (CD133 expression and Aldefluor) result in a population enriched for cells able to reconstitute tumors when implanted in immunodeficient mice, our work demonstrates that the unique ALDHhigh, low side scatter population of cells is more enriched for cells with clonogenic activity in vitro and tumor initiating activity in vivo than the CD133-positive cells. This evidence concerns the gene PROM1 and neoplasm.