In vitro studies that show a higher malignant gene expression profile and changes in astrocytoma malignant behavior in cells with higher levels of GFAPδ relative to GFAPα, as observed in neurogenic stem cells of the healthy brain (Middeldorp & Hol, 2011; Roelofs et al., 2005; van den Berge et al., 2010), further support the hypothesis of GFAP as a marker of more than lower malignant astrocytoma (Moeton et al., 2014; Stassen et al., 2017). Here, GFAP is linked to astrocytoma (excluding glioblastoma).