The majority of glioblastomas can be classified into molecular subgroups based on mutations in the TERT promoter (TERTp) and isocitrate dehydrogenase 1 or 2 (IDH). These molecular subgroups utilize distinct genetic mechanisms of telomere maintenance, either TERTp mutation leading to telomerase activation or ATRX-mutation leading to an alternative lengthening of telomeres phenotype (ALT). However, about 20% of glioblastomas lack alterations in TERTp and IDH. These tumors, designated TERTpWT-IDHWT glioblastomas, did not have well-established genetic biomarkers or defined mechanisms of telomere maintenance. The genetic landscape of TERTpWT-IDHWT glioblastoma includes tumors that have chromosomal rearrangements upstream of TERT. These rearrangements define a novel molecular subgroup of glioblastoma, that is a telomerase-positive subgroup driven by TERT-structural rearrangements (IDHWT-TERTSV).