PROM1 and cancer: There are mainly three methods for the identification of CSCs or CSC-like properties: (1) use of CSCs surface markers, such as CD44+CD24−, CD133, CD44+/EpCAM+, and CD9017, 18; (2) identifying the side population (SP) in cancer cells, which enriches CSC-like properties; and (3) determining the growth properties of cells in serum-free suspension culture19.