PROM1 and neoplasm: Tirino et al. [48] first identified CD133+ cells in osteosarcoma with stem-like features including the ability to form tumor spheres, high proliferation rate, cell cycle detection in the G2/M phase, positivity for the nuclear protein Ki-67 which is associated with cellular proliferation, SP profile and expression of ATP-binding cassette (ABC) transporters which have been implicated in chemotherapy drug resistance.