Choi and coworkers have shown the existence of a hierarchy at the level of the CD133+/ALDH+ ovarian cancer cells, where CD133+/ALDH+ ovarian cancer stem cells give rise to a population of cancer stem cells/progenitors CD133−/ALDH+ which in turn originates CD133−/ALDH− cells composed by tumorigenic/nontumorigenic cells [208]. This evidence concerns the gene PROM1 and ovarian cancer.