Glioblastoma (also called Glioblastoma Multiforme) is the most malignant astrocytic tumor (WHO grade IV) and is composed of poorly differentiated neoplastic astrocytes. Histopathological features include cellular polymorphism, nuclear atypia, brisk mitotic activity, vascular thrombosis, microvascular proliferation and necrosis. Glioblastoma typically affects adults and is preferentially located in the cerebral hemispheres. Glioblastomas may develop from diffuse astrocytomas WHO grade II or anaplastic astrocytomas ('secondary glioblastoma'), but more frequently, they manifest after a short clinical history de novo, without evidence of a less malignant precursor lesion ('primary glioblastoma'). There are two histological variants of Glioblastoma: Giant Cell Glioblastoma and Gliosarcoma. (WHO)