Biology and treatment of malignant glioma.
A large number of oncogenes have been identified as aberrant in gliomas, but only the erbB oncogene (gene encoding the epidermal growth factor receptor [EGFR]) is amplified in an appreciable number. The loss or mutation of tumor-suppressor genes located on different autosomes may be associated with progression of malignant gliomas. The p53 tumor-suppressor gene (located on chromosome 17) is frequently associated with the loss of one allele in malignant gliomas, although a large number of malignant gliomas have no p53 mutations. Some of the latter tumors have an amplified murine double minute 2 (MDM2) gene, which suppresses p53 gene activity. Genetic material from chromosome 10 may also be lost, especially in glioblastoma multiforme. In addition to the aberrant expression of EGFR, another growth factor, platelet-derived growth factor, or PDGF (ligand and/or receptors) can be overexpressed, giving cells a selective growth advantage. The blood-brain barrier is substantially altered in malignant gliomas, resulting in cerebral edema. Therapy for malignant gliomas includes surgery, radiation therapy, and chemotherapy. Surgical resection that leaves little residual tumor produces longer survival than less vigorous surgery. Radiation therapy to a dose of at least 60 Gy is required to treat malignant gliomas. Increased survival beyond that produced by standard external radiotherapy requires much larger doses; interstitial radiotherapy permits such dosing. Radiosurgery is being tested. Chemotherapy with nitrosoureas is modestly useful but appears to benefit patients with anaplastic astrocytoma more so than those with glioblastoma.