Under such conditions, however, there were similar levels of total Oct4 protein among adherent U87 parental cells, U87 tumour spheres and ITE-treated U87 tumour spheres (Fig. 3c), and only prolonged treatment with ITE could reduce the Oct4 protein levels in tumour spheres (Supplementary Fig. 30), indicating that the Oct4 proteins in stem-like cancer cells are subjected to multiple layers of regulation and are probably more stable than Oct4 in pluripotent stem cells. This evidence concerns the gene POU5F1 and cancer.