Deletion mapping of chromosome 19 in human gliomas

There is evidence that a putative glioma tumor suppressor locus resides on the long arm of chromosome 19. We present data on 161 gliomas from IS6 patients, which were studied by microsatellite analysis for loss of heterozygosity (LOH) on chromosome 19. Eight loci on the long arm and 2 loci on the short arm of chromosome IV were examined. LOH on I9qwas observed in 3/19 astrocytomas (WHO grade II), 12/27 anaplastic astrocytomas (WHO grade III), 16/76 cases of glioblastoma multiforme WHO (grade IV), 4/9 oligodendrogliomas (WHO grade II), 3/5 anaplastic oligodendrogliomas (WHO grade III), 5/9 mixed oligo-astrocytomas (WHO grade II) and 8/10 anaplastic oligo-astrocytomas (WHO grade III). While 31 of the tumors with LOH on chromosomal arm I9q exhibited allelic loss at every informative locus, 20 tumors showed terminal or interstitial deletions. In contrast to astrocytomas and glioblastomas, tumors with an oligodendroglial component had predominantly lost the entire long arm of chromosome 19. The common region of overlap in gliomas was located on 19q 13.2-q 13.4 between the markers D 19S 178 and D 19S 180. Our data confirm the involvement of a putative tumor suppressor gene on chromosomal arm 19q in gliomas and assign this gene to 19q 13.2-q 13.4.     

Allelic loss of chromosome 17p distinguishes high grade from low grade transitional cell carcinomas of the bladder

Forty-three transitional cell carcinomas of the bladder of differing grades and stages were examined for reduction to homozygosity for chromosomes 9q, 11p, and 17p. Allelic loss of chromosome 9q was seen in 24 of 38 informative grades II, III, and IV tumors providing further evidence for a bladder tumor suppressor gene on this chromosome. In contrast to the grade-independent involvement of chromosome 9q, allelic losses of chromosomes 11p and 17p were seen only in grade III and IV tumors. The results with chromosome 17p were particularly striking and showed that 0 of 10 grade II versus 20 of 31 grade III and IV tumors had allelic losses for this chromosome harboring the p53 tumor suppressor gene often mutated in other human cancers. The data suggest that cumulative genetic damage is sustained in transitional cell carcinomas and that one of the underlying molecular mechanisms distinguishing low grade from high grade tumors involves chromosome 17p.     

Absence of mutation of the p73 gene in astrocytic neoplasms

In subgroups of astrocytic neoplasms, including glioblastoma (GBM), mutations of the p53 tumour suppressor gene lead to loss of growth-suppressive properties. A p53-related gene termed p73 has recently been identified; its gene product shows structural and functional similarities to p53. After being mapped to chromosome region 1p36, p73 was proposed to act as a tumour suppressor gene, as this region is frequently deleted in a variety of human cancers, including astrocytic tumours. To determine whether p73 is involved in astrocytoma/GBM development, we analysed 10 pilocytic astrocytomas, 15 WHO grade II astrocytomas, 15 WHO grade III anaplastic astrocytomas, and 20 GBM for p73 gene alterations. In parallel, we used six polymorphic markers to determine the allelic status of region 1p36 in this tumour series. Although loss of heterozygosity was evidenced in 12 of 60 cases (20% of samples), PCR-SSCP and direct sequencing failed to detect any gene mutation in the entire coding region and intronic sequences of p73. Eight tumours displayed five distinct polymorphic nucleotide changes, also present in the corresponding normal DNA. These variations consisted of T-->C variation, with no change in Thr173; C-->T transition, with no change in His197; exon 9 simultaneous double change C-->T and T-->C , with no variations in Ala336 and His349, respectively, and C-->T change at exon 9/-24 position of intron 8. These results suggest that, in astrocytic gliomas, p73 may not play a major role as a tumour suppressor, but the relatively high incidence of LOH confirms the presence at 1p36 of an as yet unidentified gene of this category, with a key function in astrocytoma/GBM progression.     

Homozygous deletion of the p16/MTS-1/CDKN2 gene in malignant gliomas is infrequent among Japanese patients.

We have analyzed the status of the p16/MST-1/CDKN2 gene in 63 brain tumors from Japanese patients. With quantitative multiplex polymerase chain reaction (PCR) assay using the exon 2 primers of the p16 gene and control chromosome 9qSTS primers, we found homozygous deletion of the p16 gene in 7 cases; in 1 out of 10 cases of anaplastic astrocytomas (WHO grade III), 6 out of 35 cases of glioblastoma multiformes (grade IV) but in none of the tumors of grade I or II. We also found mobility-shifted PCR products in 8 cases using the single-strand conformation polymorphism technique. DNA sequencing of the aberrantly migrated products revealed that 5 cases of glioblastoma multiforme had mutations which caused amino acid substitutions. We found one case with silent mutations and two cases with nucleotide changes in the non-coding region. The frequency of the alteration of the p16 gene, either homozygous deletion or mutation accompanied with amino acid substitutions, increased in malignant brain tumors (grade III and IV) compared with that in low grade tumors (grade I and II) (p=0.0275), suggesting possible role(s) of the gene in the progression of brain tumors. In addition, the low frequency of homozygous deletions shown in this study is quite different from previous reports that demonstrated frequently deleted p16 gene in malignant gliomas from Caucasian patients. We have also shown the presence of heterogeneous cell populations within the glioblastoma masses based on the variety of the mutated p16 sequences. The present study, therefore, suggests a possible racial difference in the mechanism of the tumorigenesis and a heterogeneity of malignant gliomas developed during the tumor progression.     

p53 mutation and loss of heterozygosity on chromosomes 17 and 10 during human astrocytoma progression.

The human brain tumor, astrocytoma, typically progresses through three histopathologically defined stages with the passage of time: one premalignant stage, low-grade astrocytoma; and two malignant stages, anaplastic astrocytoma and glioblastoma multiforme. We correlated the results of a sequence analysis of the tumor suppressor gene, p53, and a restriction fragment length polymorphism analysis of chromosomes 17 and 10 in 45 patients with cerebral astrocytomas at different stages. To detect p53 mutations in tumor DNA, we analyzed polymerase chain reaction products corresponding to every p53-coding exon for single-strand conformation polymorphisms and confirmed the mutations by sequencing. Loss of heterozygosity (LOH) was determined by Southern transfer analysis of somatic and tumor DNA from these same patients using polymorphic markers for various loci on chromosomes 10 and 17. p53 mutations were found in 7 of 25 glioblastomas (28%), in 5 of 14 anaplastic astrocytomas (36%) but in 0 of 6 low-grade astrocytomas. p53 mutations were found in 62% of patients with LOH on chromosome 17p. These results indicated that p53 inactivation is a common genetic event in astrocytoma progression that may signal the transition from benign to malignant tumor stages. LOH on chromosome 10 was found in 61% of glioblastomas, in 23% of anaplastic astrocytomas, but in 0% of low-grade astrocytomas. LOH on chromosome 10 and p53 mutation were found together only in patients with glioblastoma multiforme (22%), suggesting that these genetic changes may accumulate during astrocytoma progression.     

Molecular analysis of chromosomh 1 abnormalities in human gliomas reveals frequent loss of 1p in oligodendroglial tumors

Alterations of the short arm of chromosome I are recurrently found in cytogenetic analysis of malignant gliomas, and deletions of Ip36-p32 region characterize at least the higher-grade tumors, glioblsstoma multiforme. Molecular analysis of tumor-derived and normal genomic DNA from 57 cases of gliomas, using a panel of chromosome I-specific DNA probes showed LOH in 16 tumors. Allelic losses on I p were primarily restricted to glioblastoma multiforme (2/II) and to tumors with a major oligodendroglial component: grade II oligodendrogliomas (6/6), grade III anaplastic oligodendrogliomas (5/6) and grade II-III mixed oligo-astrocytomas (2/3). Losses for Iq markers were detected in only I tumor (glioblastoma multiforme). Our data suggest that anomalies of Ip primarily characterize oligodendrogliomas, whereas they are rare events in astrocytic tumors and indicate that a tumor-suppressor gene on I p36-p32 is involved in the development of brain tumors with oligodendroglial differentiation. © 1994 Wiley-Liss, Inc.     

Roles of the functional loss of p53 and other genes in astrocytoma tumorigenesis and progression

Loss of function of the p53 tumor suppressor gene due to mutation occurs early in astrocytoma tumorigenesis in about 30-40% of cases. This is believed to confer a growth advantage to the cells, allowing them to clonally expand due to loss of the p53-controlled G1 checkpoint and apoptosis. Genetic instability due to the impaired ability of p53 to mediate DNA damage repair further facilitates the acquisition of new genetic abnormalities, leading to malignant progression of an astrocytoma into anaplastic astrocytoma. This is reflected by a high rate of p53 mutation (60-70%) in anaplastic astrocytomas. The cell cycle control gets further compromised in astrocytoma by alterations in one of the G1/S transition control genes, either loss of the p16/CDKN2 or RB genes or amplification of the cyclin D gene. The final progression process leading to glioblastoma multiforme seems to need additional genetic abnormalities in the long arm of chromosome 10; one of which is deletion and/or functional loss of the PTEN/MMAC1 gene. Glioblastomas also occur as primary (de novo) lesions in patients of older age, without p53 gene loss but with amplification of the epidermal growth factor receptor (EGFR) genes. In contrast to the secondary glioblastomas that evolve from astrocytoma cells with p53 mutations in younger patients, primary glioblastomas seem to be resistant to radiation therapy and thus show a poorer prognosis. The evaluation and design of therapeutic modalities aimed at preventing malignant progression of astrocytomas and glioblastomas should now be based on stratifying patients with astrocytic tumors according to their genetic diagnosis.     

Correlation of chromosomal imbalances by comparative genomic hybridization and expression of EGFR, PTEN, p53, and MIB-1 in diffuse gliomas

The histological subclassification of gliomas is increasingly assisted by the underlying molecular genetics which has major importance in guiding clinical management of the disease. However, the assessment of several molecular events for improving clinical care remains a challenge. Herein, we report on comparative genomic hybridization (CGH) and immunohistochemical (IHC) assessment of EGFR, PTEN, p53, and MIB-1 expression in 13 oligodendrogliomas (10 WHO grade II, 3 WHO grade III), one oligoastrocytoma (WHO grade III) and 23 high-grade astrocytomas (3 WHO grade III, 20 glioblastoma multiforme). The most frequent imbalances in oligodendroglial tumors including the oligoastrocytic case were, in decreasing order of frequency, +7q, -1p, and -4q and in astrocytomas +7q, -10q, +7p, -9p, -10p, +20q, and +20p. Some individual imbalances were associated with increasing numbers of chromosomal changes, that were +7q in both oligodendrogliomas and astrocytomas, and -9p, -10q, +20p, and +20q in astrocytomas. The markers p53 and MIB-1 were significantly higher expressed in astrocytomas than in oligodendrogliomas and expression levels of p53 and EGFR were inversely associated within the astrocytic group. In addition, p53 overexpression correlated positively with +7q and negatively with -1p in the oligodendroglial group whereas EGFR overexpression correlated positively with -1p in the oligodendroglial and positively with +7p and -10p in the astrocytic group. Short overall survival was significantly associated with +7p and -10q in astrocytomas. Collectively, these results contribute to the increasing clinical relevance of assessing tumor biological markers in gliomas.     

Brainstem gliomas--a clinicopathological study of 45 cases with p53 immunohistochemistry

BACKGROUND: Brainstem tumors represent 10% of central nervous system tumors, accounting for 30% of pediatric posterior fossa tumors. AIMS: The aim of this study was to clinicopathologically correlate 45 cases of brain stem gliomas and determine the occurrence and prognostic significance of p53 expression. MATERIALS AND METHOD: 45 cases of brain stem gliomas encountered during a 19-year period. 30 were diagnosed by surgical biopsy and 15 at autopsy. In 25 cases p53 immunohistochemistry (Avidin Biotinylated technique) was performed. The WHO brain tumor classification and Stroink's CT classification were applied. STATISTICAL ANALYSIS USED: Chi square test. RESULTS AND CONCLUSIONS: 51 % of gliomas were observed in the first decade of life. The female to male ratio was 1.04: 1. The commonest presenting features were cranial nerve palsies (33%) and cerebellar signs (29.8%). 55.55% of cases were located in the pons, 31.01% in the medulla and 13.33% in the midbrain. Diffuse astrocytomas were seen in 40 cases (5% were Grade I, 47.5%Grade II, 32.5% Grade III and 15% Grade IV) and pilocytic astrocytomas in 5 cases. Grade IV patients had 2- 3 mitoses /10 high power fields and had a poorer survival rate. Grade II astrocytomas were treated with excision and radiotherapy, while grade III and IV tumors were treated with radiotherapy and chemotherapy (CCNU). Improvement was noted in 20% of patients postoperatively. The outcome was better in patients who were treated surgically. p53 is a frequently mutated gene in brain stem astrocytomas. It was found in 50 % of glioblastoma multiforme, 28.57% of grade III astrocytoma and 12.5% of grade II astrocytoma, while grade 1 astrocytomas failed to express p53 protein. p53 positivity was more in high grade lesions, decreasing significantly in lower grade lesions.     

Molecular abnormalities of chromosome-19 in malignant gliomas - preferential involvement of the 19q13.2-q13.4 region

A deletion mapping analysis of chromosome 19 was performed on a series of 101 samples derived from malignant gliomas. A total of 35 tumors displayed different deletions for the loci studied (D19S21, D19S11, D19S74, D19S7, D19S8, CKM, and D19S22). In most instances, losses involving the long arm markers of chromosome 19 were observed, and only four samples were characterized by losses on the short arm. No tumor was found displaying loss of both short and long arm markers. The higher frequency of deletions was detected in tumors with a major oligodendroglial component: 76% of samples included in this group displayed losses at 19q. Among the astrocytic tumors, the frequency of 19q alterations varied as follows: 11% in pilocytic astrocytomas, 17% in astrocytomas grade II, 10% in anaplastic astrocytomas and 21% in glioblastoma multiforme. No ependymoma was found displaying allele loss on chromosome 19. The common region of overlap for the 19q deletions observed involves primarily the distal portion of the long arm, 19q13.2-q13.4. In agreement with previous reports, these data suggest the non-random involvement of a tumor suppressor gene located at 19q13 in the genesis or progression of malignant gliomas.     

Evidence for a tumor suppressor gene on chromosome 19q associated with human astrocytomas, oligodendrogliomas, and mixed gliomas.

Previous studies have shown frequent allelic losses of chromosomes 9p, 10, 17p, and 22q in glial tumors. Other researchers have briefly reported that glial tumors may also show allelic losses of chromosome 19, suggesting a putative tumor suppressor gene locus on this chromosome (D. T. Ransom et al., Proc. Am. Assoc. Cancer Res., 32:302, 1991). To evaluate whether loss of chromosome 19 alleles is common in glial tumors of different types and grades, we performed Southern blot restriction fragment length polymorphism analysis for multiple chromosome 19 loci in 122 gliomas from 116 patients. Twenty-nine tumors had loss of constitutional heterozygosity of 19q, and four tumors had partial deletions of 19q. Allelic losses on 19q were restricted to grade III anaplastic astrocytomas (4/9) and grade IV glioblastomas (11/46), grade II oligodendrogliomas (2/5) and grade III anaplastic oligodendrogliomas (2/2), and grade II (5/8) and grade III (5/7) mixed oligoastrocytomas. These data demonstrate genetic similarities between astrocytomas, oligodendrogliomas, and mixed glial tumors and indicate the presence of a glial tumor suppressor gene on chromosome 19q.     

Mutations of the p53 tumor suppressor gene in neoplasms of the human nervous system

A variety of neoplasms of the human nervous system were analyzed for the presence of mutations in the p53 tumor suppressor gene. DNA was extracted from frozen or formalin-fixed, paraffin-embedded material. Single-strand conformation polymorphism (SSCP) analysis for exons 5–8 was followed by direct DNA sequencing. Mutations leading to an amino acid change were found in three of 11 (27%) low-grade (World Health Organization (WHO) Grade II) astrocytomas. They were located in codon 183 (TCA → TGA) of exon 5, codon 237 (ATG → ATA) of exon 7, and codon 273 (CGT → CAT) of exon 8. In one of these cases, the sequence indicated loss of the wild-type allele. Of 12 juvenile pilocytic astrocytomas (WHO Grade I), none contained a p53 mutation, suggesting a different molecular basis for this childhood neoplasm. Except for a mutation in one of seven (14%) meningeal hemangiopericytomas (codon 238; TGT → TTT, Cys → Phe), no mutations were observed in exons 5–8 of the p53 gene in any of the following tumors of the nervous system and its coverings: 13 schwannomas, 12 central neurocytomas, 22 meningiomas, 10 choroid plexus papillomas and carcinomas, and 30 neuroblastomas of the sympathetic nervous system. These and published data support the view that p53 mutations are frequently involved both in low-grade and progressive (anaplastic) astrocytomas, including glioblastomas multiforme. Oligodendrogliomas, medulloblastomas, meningiomas, and hemangiopericytomas rarely (<15%) show p53 mutations in exons 5–8, whereas none of the remaining nervous system neoplasms revealed evidence of an involvement of the p53 gene in their development.     

Chromosome 10 and 17 deletions and p53 gene mutations in Thai patients with astrocytomas

The tumor suppressor gene locus is known to be partly responsible for the tumorigenesis of sporadic gliomas, but the genetic events that drive the neoplastic process of this tumor remain largely unknown. We correlated the results of loss of heterozygosity (LOH) analysis on chromosomes 10 and 17 and a point mutation analysis of a tumor suppressor gene, p53, in 21 patients with astrocytomas at different stages. LOH was determined in tumor and leukocyte DNAs of primary human central nervous system tumors. The incidence rate of brain tumors corresponded to every p53-coding exon for single-strand conformation polymorphisms (SSCP) and the mutations were confirmed by sequencing. p53 mutations were found in 2 of 10 glioblastomas (20%) and in 1 of 8 low-grade astrocytomas (12.5%). Similarly, LOH on chromosome 10 was also found in 2 of 10 glioblastomas (20%) and 1 of 8 low-grade astocytomas (12.5%). Neither of the p53 mutations nor LOH on chromosome 10 was observed together in the tumor types analyzed. Interestingly, the p53 mutations were found in 29% of patients with LOH on chromosome 17. The fact that p53 mutation and LOH on chromosome 17 were found together only in glioblastomas, suggested that these genetic changes may accumulate during astrocytoma progression.     

Molecular genetic investigation of sporadic renal cell carcinoma: analysis of allele loss on chromosomes 3p, 5q, 11p, 17 and 22.

To investigate the role of tumour-suppressor genes on the short arm of chromosome 3 in the mechanism of tumorigenesis in non-familial renal cell carcinoma, we analysed 55 paired blood-tumour DNA samples for allele loss on chromosome 3p and in the region of known or putative tumour-suppressor genes on chromosomes 5, 11, 17 and 22. Sixty-four per cent (35/55) of informative tumours showed loss of heterozygosity (LOH) of at least one locus on the short arm of chromosome 3, compared with only 13% at the p53 tumour-suppressor gene and 6% at 17q21. LOH at chromosome 5q21 and 22q was uncommon (2-3%). Detailed analysis of the regions of LOH on chromosome 3p suggested that, in addition to the VHL gene in chromosome 3p25-p26, mutations in one or more tumour-suppressor genes in chromosome 3p13-p24 may be involved in the pathogenesis of sporadic renal cell carcinoma (RCC). We also confirmed previous suggestions that chromosome 3p allele loss is not a feature of papillary RCC (P < 0.05).     

Evidence for the involvement of a potential second tumor suppressor gene on chromosome 17 distinct from p53 in malignant astrocytomas.

Molecular analysis of malignant astrocytomas demonstrated three distinct groups of tumors with chromosome 17p abnormalities, which include (a) deletion of the p53 locus (17p13.1) and mutations in the remaining allele, (b) deletion of the p53 locus but no detectable mutations in the remaining allele, and (c) deletions not including the p53 locus but mutations in one of the alleles. Furthermore, deletion mapping analysis demonstrated allelic loss of genes distal to D17S28/D17S5 markers (17p13.3) in group C tumors. The loss of heterozygosity of genes on chromosome 17 without detectable mutation (group B) or deletion (group C) in the p53 gene implies the presence of a second tumor suppressor gene in the telomeric region of 17p, the homozygous functional inactivation of which may play a role, either alone or in conjunction with p53, in the initiation and/or progression of astrocytic neoplasms.     

Infrequent p53 gene mutations in medulloblastomas

Cytogenetic and molecular studies of medulloblastomas have demonstrated frequent loss of sequences from the short arm of chromosome 17, possibly implicating loss or inactivation of the p53 tumor suppressor gene. We amplified exons 5 through 8 of the p53 gene by the polymerase chain reaction technique. These segments, which encompass the regions usually mutated in human tumors, were sequenced to search for p53 mutations in 12 medulloblastoma tumors, 8 xenografts, and 3 permanent cell lines. Mutation of the p53 gene was found in only 1 of 3 cell lines tested and in none of the xenografts or primary tumors studied. Our results suggest that p53 is mutated in an unusual way or that a second tumor suppressor gene on the short arm of chromosome 17 is involved in the pathogenesis of medulloblastoma.     

Allelic loss of chromosome 1p and radiotherapy plus chemotherapy in patients with oligodendrogliomas

INTRODUCTION: Allelic loss of the short arm of chromosome 1 predicts radiographic response to chemotherapy and long overall survival times in patients with anaplastic oligodendrogliomas. Using a database of patients with oligodendrogliomas in whom chromosome 1p status was known, we explored whether allelic loss of 1p also predicted longer duration of tumor control when radiotherapy was part of the initial treatment of these patients. MATERIALS AND METHODS: We measured progression-free survival following radiotherapy in a cohort of patients with World Health Organization (WHO) Grade II and WHO Grade III oligodendrogliomas. The effects on progression-free survival of patient age, Karnofsky performance score (KPS), tumor grade when irradiated and chromosome 1p status were examined by univariate and multivariate statistical analyses. For the subset of patients with newly diagnosed anaplastic oligodendrogliomas, relationships between use of chemotherapy, chromosome 1p status and progression-free survival were also examined. RESULTS: Fifty-five patients (29 male, 26 female; ages 18-75 years; median, 44 years; KPS 50-90, median 80) were irradiated for either a WHO Grade II (n = 19) or Grade III (n = 36) oligodendroglioma. Twenty-eight patients had chemotherapy immediately prior to radiotherapy, and 27 had chemotherapy at progression following radiotherapy. The median radiation dose was 54 Gy in 30 fractions. Loss of heterozygosity (LOH) at chromosome 1p was evident in 36 tumors and absent in 19. Overall median progression-free survival after radiotherapy was 40.4 months. Median progression-free survival was 55.0 months for patients whose tumors harbored 1p loss vs. 6.2 months for those patients whose tumors retained both copies of chromosome 1p (p < 0.001). On both univariate and multivariate analyses, chromosome lp loss was the principal independent predictor of longer progression-free survival for patients with Grade II and III oligodendrogliomas. For Grade III oligodendrogliomas, chemotherapy as an adjunct to radiotherapy prolonged tumor control for those patients whose tumors harbored allelic loss of chromosome 1p (p = 0.004). CONCLUSION: These data suggest allelic loss of chromosome 1p in patients with oligodendroglial neoplasms predicts longer progression-free survival among patients receiving radiotherapy +/- chemotherapy as part of their initial treatment. Chromosome 1p loss may be an important stratification variable in future therapeutic trials of oligodendroglioma.     

Methylation of O6-methylguanine DNA methyltransferase and loss of heterozygosity on 19q and/or 17p are overlapping features of secondary glioblastomas with prolonged survival.

PURPOSE: Recent data suggest that methylation of the DNA repair gene O(6)-methylguanine DNA methyltransferase (MGMT), by increasing the chemosensitivity of glioblastoma multiforme, is significantly associated with improved prognosis. Results in contradiction with these findings, however, are present in the literature and the clinical and genetic context framing MGMT methylation is poorly characterized. EXPERIMENTAL DESIGN: To address these issues, we have investigated the MGMT methylation status, clinical and magnetic resonance imaging characteristics, and relevant genetic features (loss of heterozygosity on 17p and 19q, EGFR amplification, and p53 mutations) in a retrospective study on 86 patients affected by glioblastoma multiforme: 72 patients had a clinical history indicating de novo insurgence of the tumor and the remaining 14 were secondary glioblastoma multiforme. RESULTS: MGMT methylation was detected by methylation-specific PCR in 41 of 86 cases (47.7%; Meth+). Progression-free survival and overall survival were significantly longer in Meth+ than in Meth- patients [10 versus 7 months (P=0.003, log-rank test) and 18 versus 14 months (P=0.0003, log-rank test), respectively]. Mixed-nodular enhancement at magnetic resonance imaging was significantly more frequent in Meth+ and secondary glioblastoma multiforme and ring enhancement in Meth- and primary glioblastoma multiforme (P<0.005). MGMT methylation was more present in secondary glioblastoma multiforme (P=0.006) and associated with loss of heterozygosity on 17p and/or 19q (P=0.005). CONCLUSIONS: These observations suggest that MGMT methylation is part of a genetic signature of glioblastomas that developed from lower-grade gliomas.     

Loss of heterozygosity for loci on chromosome 17p in human malignant astrocytoma

Loss of constitutional heterozygosity for specific chromosomal loci, when found consistently in a particular tumor type, suggests that a recessive oncogene important in the genesis of that tumor may be present within the involved chromosomal loci. DNA markers that detect restriction fragment length polymorphisms are powerful tools that have been used to detect loss of chromosomal loci in a growing number of human malignancies. The human brain tumor astrocytoma is usually malignant and virtually incurable. Two types of malignant astrocytomas are recognized histopathologically:anaplastic astrocytoma and glioblastoma multiforme. We carried out a restriction fragment length polymorphism analysis of tumors from 15 patients with anaplastic astrocytoma and 20 patients with glioblastoma using polymorphic DNA markers for loci on chromosome 17. Loss of constitutional heterozygosity for loci on chromosome 17 was found in both anaplastic astrocytoma and glioblastoma patients with equal frequency (40% of cases). Our mapping data revealed a region of loss on chromosome 17p between physical loci p11.2 and pter that was common to both patient groups. Taken together with the previously reported finding of loss of heterozygosity for loci on chromosome 10 in glioblastoma, these results indicate that tumorigenesis in the astrocyte lineage may involve recessive oncogenes on two different chromosomes.