GFAP and glioblastoma: Similar to the higher proportion of tumor cells expressing the NSC-associated protein SOX2 and in contrast to the lower proportion of tumor cells expressing the astrocytic marker GFAP in GSCs in serum-free conditions, FOXM1 (+) cells were predominantly detected in GSCs in serum-free medium (GBM NSs), when compared to GBM cells propagated in serum-containing medium (SPGCs) (Fig. 2H; Supporting Information Fig. S5).