MGMT and glioblastoma: In glioblastoma (GBM), ALDH1A1 expression above vs below the mean causes temozolomide and radiation resistance and is associated with a substantial reduction in survival (methylated MGMT 14.6 vs 32.9 months, P = .004; unmethylated MGMT: 12.6 vs 21.4 months P = .005), while knockdown of ALDH1A1 restores sensitivity to chemotherapy and radiation therapy.1,2 ALDH1A1 is also a known mediator of resistance to EGFR (epidermal growth factor receptor) blockade and an activator of HIF1A.