In comparison to normal tumor cells, CSCs are less sensitive to activation of cell death58 and previous studies from our group also demonstrated that BAG3 exerts pronounced antiapoptotic effects, as demonstrated by increased resistance to the BH3 mimetic ABT‐737 (Venetoclax) in therapy‐resistant TNBC59 and in GBM,16 the latter finding now being confirmed in an organotypic brain slice transplantation model of GBM (Figure S2A–C). Here, BAG3 is linked to glioblastoma.