IDH1 and glioma: IDH mutations are rare in GBM developing in older patients who usually carry EGFR and PTEN alterations (primary GBM), (Figure 2, N. 2), but are present in a large proportion of low-grade glioma and, along with TP53 mutations, in high-grade glioma that evolved from low–grade tumors (secondary glioblastoma) (35) Figure 2, N. 3 and 4).