Chapter 57

## Abstract

Abstract

1. Glioblastoma multiforme, the most common malignant primary brain tumor of adults, is characterized by gains of chromosome 7 and losses of chromosome 10, which are seen in up to 80 to 90 percent of patients. Approximately 25 to 30 percent of patients with loss of chromosome 10 have mutations of the PTEN/MMAC1 gene. More than half of these tumors also contain abnormalities of genes involved in cell cycle control. Specifically, about a third of patients have homozygous deletions of the CDKN2A gene, while some tumors with intact CDKN2A have loss of expression of the retinoblastoma gene or have amplification of the CDK4 gene. In addition, approximately one-half of patients have amplification, often with rearrangement, of the epidermal growth factor receptor (EGFR) gene.

2. Low-grade astrocytomas, particularly anaplastic astrocytomas, as well as low-grade tumors that progress to glioblastomas, contain mutations of the TP53 gene in up to 50 percent of patients in some series.

3. Oligodendrogliomas are frequently characterized by losses of 1p and 19q. The target genes for loss of these regions remain unknown.

4. A subset of ependymomas has loss of 22q. Mutation of the neurofibromatosis type 2 (NF2) gene has been described in a single patient with an ependymoma. Therefore, whether or not this gene is the target of the 22q loss in these tumors remains speculative.

5. The most consistent finding in medulloblastomas, the most common primary malignant brain tumor of children, is loss of 17p. Mapping of the deleted region to distal 17p and a low incidence of TP53 gene mutations suggest that TP53 is not the target of 17p loss in these tumors. Approximately 15 percent of patients have mutations of the PTCH gene, in association with loss of 9q. The incidence of gene amplification has variously been reported to be from less than 5 to 22 percent in medulloblastomas. The amplified gene is usually c-myc, with a few examples of N-myc gene amplification.

6. Approximately 60 percent of meningiomas and schwannomas have loss of 22q, which is usually associated with NF2 gene mutations.

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