Given that our recent study identified C/EBPβ as a key transcriptional factor for CD109 expression11 and that analysis of our matched longitudinal GBM samples indicated that C/EBPβ was significantly higher in CD109up recurrence group (Supplementary Fig. 5b), we examined whether occupancy of C/EBPβ at the promoter region of CD109 is under the control of HDAC1 in core-like spheres. Here, HDAC1 is linked to glioblastoma.