EGF and glioblastoma: As the EGFR (HER1) has been (i) proposed as a GBM subtype maker [16, 20, 21], (ii) the EGFR is typically expressed in activated adult neural stem cells and progenitors [53], and (iii) EGF is one of the two growth factors present in the serum-free N-medium used for SLGC cultures [22, 23] we investigated the role of the EGFR in more detail.