In agreement with this hypothesis, higher expression of PTGER4 is observed in the tumour bulk of GBM18 and in the TCGA GBM cohort (Fig. S9a) as compared to GIC18, and a negative correlation was observed between the expression of PTGER4 and PROM1 (CD133), a GIC marker, in the TCGA datasets (Fig. S9b). Here, PTGER4 is linked to glioblastoma.