Abstract BACKGROUND Multiple clinical aspects and accumulating indirect and direct experimental data are providing evidence that the supratentorial brain parenchyma becomes entirely and quiescently micro-infiltrated long before primary tumor bulk growth. Two diffuse micro-infiltrations occur in IDH-wildtype glioblastoma, the first long before primary bulk growth (the only one effective in giving rise to distant relapses) and the second, well known but ineffective, during bulk growth and evolution. Furthermore, they clearly indicate that there are two causes of therapeutic resistance, the second never yet therapeutically challenged. MATERIAL AND METHODS The collection of separate multiregional samples in the tumor bulk enabled us to reconstruct the phylogenetic tree of the primary tumor mass. However, the therapeutic solution to IDH-wildtype glioblastoma lies in the micro-infiltrated brain where the ancestral founder CSCs reside quiescently (they are invariably extinct in the tumor bulk at the time of diagnosis). We are using the four ethical methods, as part of normal glioblastoma surgery, to sample the micro-infiltrated brain parenchyma to identify and deeply characterize the dormant ancestral founder CSCs. RESULTS In the bulk, multiple separated samples allowed us to infer the phylogenetic tree of the tumor as well as driver and passenger events and the CSC variants. The ethical methods to sample the micro-infiltrated brain parenchyma are enabling us to identify and characterize the ancestral founder CSCs, which hibernate in the perivascular parenchymal niches of the supratentorial brain (their activation being the only cause of distant recurrences). CONCLUSION The first cause of therapeutic resistance is due to intratumor heterogeneity and the second to the silent presence in the whole supratentorial brain of quiescent founder CSCs. The IDH-wildtype glioblastoma is the only brain tumor that arises from the III layer of the SVZ and it is able to disseminate widely across the supratentorial brain parenchyma before starting its growth. Only the identification and characterization of the ancestral founder CSC will enable us to simultaneously overcome both causes of resistance and provide a therapeutic solution to this dreadful malignancy. Indeed, the ancestral founder CSC is identical to the premalignant progenitor of the SVZ and to the cell that activated in one (or more) brain location, gave rise to the primary tumor bulk(s) and transmitted the ancestral driver genomic alterations to all subsequent evolutionary CSC variants.