TP53 and astrocytoma (excluding glioblastoma): Furthermore, tumors with mutations in P53 (TP53), a major tumor suppressor gene [38], and α-thalassemia/mental-retardation-syndrome-X-linked (ATRX), which is involved in chromatin remodeling pathways and regulation of telomeres [39,40,41], are classified as astrocytoma, IDH-mutant.