Although both CD133+ and CD133- cells are capable of tumor initiation in the nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice, most of CD133+ tumor subpopulations form colonospheres in an in vitro culture and retain long-term tumorigenic capacity in a NOD/SCID serial xenotransplantation model [41]. This evidence concerns the gene PROM1 and neoplasm.