On a three-dimensional glioblastoma explant model that mimics the tumor’s cytoarchitecture and stroma, Notch inhibition through GSIs led to a loss in the number of endothelial cells and also to the downregulation of Notch target genes (HES1 and HES5) and also eliminated the expression of the endothelial marker CD105. Here, HES1 is linked to neoplasm.