ATRX loss is associated with alternative lengthening of telomeres, a hallmark of genomic instability, and is predominantly observed in LGGs with IDH mutations and without 1p/19q codeletion.107 Although rare in adult primary GBM, ATRX mutations are more prevalent in younger patients and secondary GBMs, where they correlate with improved prognosis. This evidence concerns the gene IDH1 and glioblastoma.