(Refer to the Anaplastic Astrocytomas section of this summary for treatment information.)
Glioblastoma (WHO grade IV), also known as glioblastoma multiforme, may develop from a diffuse astrocytoma or an anaplastic astrocytoma but more commonly presents de novo without evidence of a less malignant precursor. Histologically, this tumor is an anaplastic, cellular glioma composed of poorly differentiated, often pleomorphic astrocytic tumor cells with marked nuclear atypia and brisk mitotic activity. Secondary glioblastoma is the term used to describe a glioblastoma developed from a diffuse astrocytoma or an anaplastic astrocytoma. Glioblastoma is the most frequent brain tumor and accounts for approximately 12% to 15% of all brain tumors and 50% to 60% of all astrocytic tumors. The peak incidence occurs between the ages of 45 and 70 years. Glioblastoma primarily affects the cerebral hemispheres. Two histologic variants include: giant cell glioblastoma and gliosarcoma. Glioblastoma has been associated with more specific genetic abnormalities than any other astrocytic neoplasm, but none are specific to it. Amplification of the epidermal growth factor receptor locus is found in approximately 40% of primary glioblastomas but is rarely found in secondary glioblastomas; mutations of the PTEN gene are observed in 45% of primary glioblastomas and are seen more frequently in primary glioblastomas than in secondary glioblastomas. Loss of heterozygosity (LOH) of chromosome 10 and loss of an entire copy of chromosome 10 are the most frequently observed chromosomal alterations. Glioblastomas are seen in mismatch repair-associated Turcot syndrome type 1. Glioblastomas are among the most aggressively malignant human neoplasms, with a mean total length of disease in patients with primary glioblastoma of less than 1 year. Mutation of the PTEN gene is associated with a poor prognosis in a subset of patients with gliomas.
(Refer to the Glioblastoma section of this summary for treatment information.)
Pleomorphic xanthoastrocytoma (WHO grade II) is a rare astrocytic tumor composed of pleomorphic and lipidized cells expressing glial fibrillary acidic protein (GFAP). This tumor accounts for fewer than 1% of all astrocytic neoplasms, typically develops in children and young adults, and commonly involves the cerebrum and meninges. This tumor has a relatively favorable prognosis; recurrence-free survival rates of 72% at 5 years and 61% at 10 years have been reported. No specific cytogenetics or molecular genetics exist with this tumor.
Subependymal giant cell astrocytoma (SEGA) (WHO grade I) is a benign, slow-growing tumor typically arising in the wall of the lateral ventricles and composed of large ganglioid astrocytes. SEGA occurs almost exclusively in patients with tuberous sclerosis complex (TSC); its incidence ranges from approximately 6% to 16% of patients with TSC. SEGA typically occurs during the first 2 decades of life. Genetic linkage studies indicate two distinct TSC loci on chromosome 9q (TSC1) and on chromosome 16p (TSC2). Its relationship with astroglial tumors remains unclear.