MGMT and glioblastoma: Favorable prognostic biomarkers carried within GBM-derived exosomes were considered the MGMT (O(6)-methylguanine DNA methyltransferase) and APNG (alkylpurine-DNA-N-glycosylase), which are the crucial enzymes able to repair TMZ-induced DNA damage, and their levels in tissues are inversely correlated with the therapy efficacy, while their expression is correlated with chemo-resistance [169].