Using isogenic derivatives of glioblastoma U87 cells (ATCC# HTB-14), some investigators have determined that the wild-type (WT) tumor suppressor gene p53 promotes radiosensitivity to fractionated RT (Gupta et al., 1996; Haas-Kogan et al., 1996, 1999; Yount et al., 1996, 1998) by maintaining the integrity of the cell-cycle G1-checkpoint (independent of apoptosis). This evidence concerns the gene TP53 and glioblastoma.