The most malignant astrocytic tumor (WHO grade IV). It is composed of poorly differentiated neoplastic astrocytes and it is characterized by the presence of cellular polymorphism, nuclear atypia, brisk mitotic activity, vascular thrombosis, microvascular proliferation and necrosis. It typically affects adults and is preferentially located in the cerebral hemispheres. It may develop from diffuse astrocytoma WHO grade II or anaplastic astrocytoma (secondary glioblastoma, IDH-mutant), but more frequently, it manifests after a short clinical history de novo, without evidence of a less malignant precursor lesion (primary glioblastoma, IDH- wildtype). (Adapted from WHO). The disease is Monarch Disease Ontology identifier MONDO_0018177 (glioblastoma). Also known as: GBM, GBM (glioblastoma), WHO grade IV glioma, glioblastoma (disease), glioblastoma multiforme, glioblastoma multiforme (disease), grade IV astrocytic neoplasm, grade IV astrocytic tumor.