This suggests that not only does the p21/Cdk2 ratio play a role in the maintenance of senescence following irradiation, but that there may be a sex difference in sensitivity to p21/Cdk2 levels and/or that p21 may be playing a greater role in irradiation-induced senescence in female GBM cells than in male GBM cells. The gene discussed is CDKN1A; the disease is glioblastoma.