POU5F1 and cancer: Reduction of endogenous ITE levels in cancer cells by tryptophan deprivation or hypoxia led to Oct4 elevation and augmented cancer cell stemness (Supplementary Fig. 41), indicating that the silenced expression of Oct4 in differentiated cancer cells is still (at least partially) activatable and that stemness may be a rather general and flexible quality of tumour cells24, 25.