MGMT and glioblastoma: In several small retrospective studies, ctDNAs were successfully detected in GBM patients and multiple molecular alterations were characterized including loss of heterozygosity (LOH) in chromosome arms 1p, 19q and 10q, IDH1, and EGFRvIII mutations as well as methylation of promoters of MGMT, PTEN, and CDKN2A [103–105].