PROM1 and cancer: Whereas flow cytometry using the surface markers CD133, EpCAM, and CD44 already suggested that the cancer stem cell content was strongly reduced, functional assays (e.g. sphere formation assay) validated that the cells isolated from the explanted tumors indeed were unable to form tumor spheres in vitro, strongly suggesting that the cancer stem cell population as the root of the disease, had been effectively targeted by the triple combination.