IDH1 and glioblastoma: Alteration of specific GBM markers, including the O(6)-methylguanine-DNA methyltransferase (MGMT) promoter methylation, epidermal growth factor receptor (EGFR) overexpression, co-deletion of 1p and 19q, mutation in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) as well as telomerase reverse transcriptase gene (TERT) promoter, along with epigenome analysis not only underline the novel nomenclature but have a prognostic value and may guide treatment decisions.