PROM1 and neoplasm: It has been reported that CSCs express unique surface markers (e.g., CD24, CD26, CD44, CD90, CD133, and CD166), exist in a side-population (SP) fraction that possesses increased Hoechst-33342 efflux capacity, exhibit high aldehyde dehydrogenase-1 (ALDH1) activity, form spheres when cultured in non-adherent conditions [3,5], and show high tumorigenic potential when xenografted as tumor in immunodeficient mice [2,3].