During the formation and expansion of the U87 tumour spheres (Supplementary Fig. 27), there was a gradual increase in the POU5F1 transcript levels starting from 24 h (Supplementary Fig. 28, Fig. 3b), a point at which no endogenous ITE from the tumour spheres can be detected (Supplementary Fig. 29). Here, POU5F1 is linked to neoplasm.