GBM was classified as either primary (arises de novo, IDH wild type, with mutations in telomerase reverse transcriptase [TERT], epidermal growth factor receptor [EGFR], and phosphatase and tensin homolog [PTEN]), or secondary (progresses from a grade II or III astrocytoma, IDH mutant, with mutations in tumor protein 53 [TP53], and alpha-thalassemia/mental retardation syndrome X-linked [ATRX] gene). The gene discussed is ATRX; the disease is astrocytoma (excluding glioblastoma).