Our findings show that Pen-d/n-ATF5-RP enters and promotes apoptotic activity in cultured glioblastoma cells, including glioma stem cells, and that when systemically administered to animals, crosses the blood brain barrier, enters brain and tumor cells and causes massive tumor cell death and long-term tumor regression/eradication without apparent harm to normal tissues. This evidence concerns the gene ATF5 and glioblastoma.