GENETIC ALTERATIONS IN MULTIFOCAL PRIMARY BRAIN TUMORS

我们注意到，多灶性神经胶质瘤，在近10年前是罕见的

We have noticed that multifocal glioma, a rarity almost 10 years ago, has been increased dramatically in frequency over the last few years. Moreover, we found increased incidence of second malignancies in patients with multifocal disease indicating possible genetic abnormalities. Recent evidence suggests that abnormalities of two negative-growth regulatory genes, the neurofibromatosis type 1 (NF1) and p53 genes, and the positive-growth regulatory gene, epidermal growth factor receptor gene (EGFR), may be involved in the development of malignant brain tumors. The first aim of this project is designed to examine the diverse somatic alterations of p53, NF1,and EGFR genes as well as germ line 53 gene mutations in patients with multifocal gliomas and unifocal gliomas with either second malignancies or strong family history of cancer. In addition, tumor tissue from multifocal gliomas will be examined from at lest two different sites and from second malignancies in order to examine the monoclonal versus polyclonal origin of multifocal glioma formation. Family members of patients with germline mutations will also be tested and offered genetic counseling. Our group has found that the NF1 gene has two different types of transcripts (type I and type II) in the GAP related domain (GRD), the differential expression of which might be functionally involved in the differentiation of neuroectodermal cells. The second aim is directed at testing the hypothesis that differential expression of type I and type II transcripts is correlated with the malignancy, multifocality, and incidence of second tumors in patients with malignant gliomas. Recently, a method has been described that allows the identification of differently expressed genes in various cells using the polymerase chain reaction in order to separate and clone individual mRNAs. The third aim of this project is the application of this technique to investigate the presence of other unknown yet oncogenes or suppressor genes in this unique subgroup of surgically removed multifocal gliomas, gliomas associated with second malignancies and gliomas in patients with strong familial cancer history. This study will improve our understanding of the implication of p53, NF1, and EGFR genes in the neuroectodermal malignant transformation and progression and may yield information to help in identifying family members at risk for development of malignancies. Furthermore, it is expected that unknown yet oncogenes and suppressor genes will be discovered, and the accumulated events leading or contributing to neoplastic transformation of the neural tissue elucidated. Results of this study could open new avenues in attempts to reverse the malignant phenotype with genetic manipulation.