Molecular pathogenesis of astrocytic tumours

Our current knowledge of the molecular pathogenesis of the diffuse adult astrocytic tumours is vast if compared to 20 syears ago, yet we are far from understanding the details of this process at the molecular level and using such an understanding to logically and specifically treat patients' tumours. In other astrocytic tumours we have little or no knowledge of the molecular processes. This article will attempt to summarise the histological classification criteria and genetic data for all the astrocytic tumours. The current World Health Organisation classification lists six entities, some with subgroups. Common problems associated with the diagnosis of these tumours are outlined. While the molecular findings are not as yet used clinically, we are approaching a time when the histological investigation will have to be supplemented with molecular data to ensure the best choice of treatment for the patient and as an accurate indicator of prognosis.     

Molecular markers of prognosis in astrocytic tumors

BACKGROUND: Astrocytoma is a primary brain tumor that affects 20,000 Americans each year. To date, only age and histologic grade stand out as independent predictors of survival. There is now increased interest in the use of molecular markers as objective standards against which to establish diagnosis and grade. METHODS: The study evaluated human glioma tumor suppressor genes and associated loci in fresh snap-frozen gliomas from 63 males and 37 females, with a median age of 42 years, including 19 low-grade astrocytomas. The tumor samples were selected so that about equal numbers of glioblastomas from younger and older patients were represented in the series. Methods for suppressor gene and genetic loci evaluation included loss of heterozygosity (LOH) analysis, multiplex polymerase chain reaction analysis, and gene sequencing. RESULTS: Low-grade astrocytomas had the least number of molecular abnormalities. LOH on 9p and/or CDKN2A deletion occurred more often in glioblastomas (P < 0.001), LOH on 17p/TP53 mutations occurred more frequently in anaplastic astrocytomas (AAs; P = 0.112), and LOH on 10q/PTEN mutation frequency was similar in glioblastomas and AAs (P < 0.001). Poorer survival was associated significantly with the occurrence of either deletion of p16 (P = 0.031), LOH on 9p (P = 0.016), or LOH on 10q (P = 0.0007). The absence of LOH on 17p and the presence of PTEN mutation were associated marginally with survival. Even though TP53 mutations were more frequent among younger patients with glioblastoma, they had no statistically significant effect on survival after adjustment for age (P = 0.62). In all multivariate models, age and grade were the only significant predictors of survival or were nearly significant predictors of survival. CONCLUSIONS: The results suggest that LOH on 9p and p16 deletions may prove to be objective standards for the diagnosis of patients with high-grade gliomas, although the absence of these abnormalities is nonprognostic.     

Proliferative potential and outcome in pediatric astrocytic tumors

Summary In 43 pediatric patients (29 male, 14 female) with primary astrocytic tumors of the central nervous system (CNS), the correlation was evaluated between outcome and proliferative potential, measured by the bromodeoxyuridine (BrdU) labeling index (LI). Twenty-five patients had low-grade gliomas, 13 had anaplastic gliomas, and 5 had glioblastomas multiforme (GBM). All patients underwent surgery; 37 also had chemotherapy, radiation therapy, or both. The median BrdU LIs were < 1% (range 0–9.3%) in low-grade gliomas, 2.3% (range 0–21.2%) in anaplastic gliomas, and 7.7% (range 0–21.3%) in GBM. Seven of eight patients with BrdU LI > 5% have died (median survival 29 weeks). Median survival has not been reached in patients with BrdU LI <1% (19/22 alive) or between 1% and 5% (12/13 alive) after median follow-up periods of 165 and 120 weeks, respectively. A high BrdU LI correlated with short survival (p = 0.0001); the association between malignant histology and short survival was weaker (p = 0.019). BrdU LI is therefore a significant predictor of outcome in patients with primary CNS astrocytomas and appears to be a stronger predictor than histology in patients with low-grade and anaplastic gliomas. More patients need to be studied to confirm these preliminary observations. Address for offprints: M.D. Prados, Department of Neurological Surgery, c/o The Editorial Office, 1360 Ninth Avenue, Suite 210, San Francisco, CA 94122, USA     

Molecular pathogenesis of oligodendroglial tumors

Based on their histopathological appearances, most diffusely infiltrative gliomas can be classified either as astrocytic tumors (As), pure oligodendroglial tumors (Os) or mixed oligoastrocytic tumors (OAs). The latter two may be grouped together as oligodendroglial tumors (OTs). The distinction between As and OTs is important because of the more favorable clinical behavior of OTs. Unfortunately, the histopathological delineation of OAs, Os and As can be difficult because of vague and subjective histopathological criteria. Over the last decade, the knowledge on the molecular genetic background of OTs has drastically increased. This review provides an overview of molecular genetic aberrations in OTs and discusses the pathobiological and clinical significance of these aberrations. In contrast to As, OTs frequently show frequent loss of heterozygosity on chromosome arms 1p and 19q. Since these aberrations are significantly correlated with clinically relevant parameters, such as prognosis and chemosensitivity, and given the difficulties in histopathological typing and grading of glial tumors, genetic testing should be included in routine glioma diagnostics. It is to be expected that the identification of the relevant tumor suppressor genes located on 1p and 19q will lead to more refined genetic tests for OTs. Furthermore, as microarray technology is rapidly increasing, it is likely that clinically relevant markers for OTs will be identified on other chromosomes and need to be included into routine glioma diagnostics as well.     

The frequency of NBN molecular variants in pediatric astrocytic tumors

Gliomas, particularly those of astrocytic origin, are the most frequent primary central nervous system tumors that develop in children. The majority of them are benign and slow growing, with relatively good prognosis. Several genomic and gene alterations are known to be involved in astrocytoma development, but the precise mechanisms remain poorly understood. The NBN gene, which participates in DNA double-strand break repair and maintenance of genome stability, has been postulated to be a susceptibility factor for a number of cancers. Here we report the results of NBN gene analyses performed in 127 children with various astrocytic tumors. PCR-SSCP analysis followed by DNA sequencing was used for molecular variant screening. Three carriers (2.37%) of different germline mutations on one NBN allele were found. The common Slavic deletion c.657_661del5 (p.K219fsX19) was detected in a patient with pilocytic astrocytoma; a known mutation, c.643C>T (p.R215W), and a new substitution, c.565C>G (p.Q189E), were identified in two patients with primary glioblastoma. The risk of developing astrocytic malignancies is estimated to be 1.33 times higher for c.657_661del5 and 3.2 times higher for c.643C>T than in the general Polish population (P > 0.05). Because of the low frequency of the mutations identified in the studied group, we were unable to determine the exact role of NBN in the development of astrocytoma in children. The presence of two potentially pathogenic NBN molecular variants among 16 glioblastoma cases (12.5%) could be a remarkable finding in our study. We thus cannot exclude a possible role of NBN in the tumorigenesis of a certain type of astrocytic tumors.     

Molecular pathogenesis of childhood brain tumors

In the last decade, the molecular biology revolution has advanced considerably. These advances have enhanced our understanding of the genetic underpinnings of human brain tumors in general, and pediatric brain tumors in particular. We now know that many pediatric brain tumors arise from disturbances in developmentally regulated signaling pathways. The medulloblastoma, a tumor in which the developmental Hedgehog and WNT pathways have gone awry, is a prime example of this. New techniques in genetic engineering have allowed for the creation of sophisticated mouse models of brain tumors that recapitulate the human disease. Many laboratories are now using cDNA microarrays to study the expression level of thousands of genes that may be aberrantly expressed in brain tumors when compared to normal control cells. In the next decade, the use of several new molecular techniques to establish brain tumor diagnoses will likely become standard tools in the diagnostics and treatment stratification of children with central nervous system tumors.     

Molecular analysis of pediatric brain tumors

The identification of molecular genetic abnormalities in specific types of pediatric brain tumors is beginning to play a role in the stratification of patients into treatment groups. The finding of an INI1 alteration in an atypical teratoid/ rhabdoid tumor or malignant neoplasm with overlapping histologic features will be required for entry onto diseasespecific protocols within the Children’s Oncology Group. Refinement in the classification of medulloblastoma and malignant glioma patients will likely depend on the genetic and signaling pathways that characterize these tumors. Advances in this area will depend on the ability to identify new disease genes, validate prognostic markers, and develop biologically based therapeutic strategies to tailor treatment.     

Molecular pathogenesis of MEN2-associated tumors

Although the gene responsible for multiple endocrine neoplasia type 2 (MEN2) was discovered many years ago, the exact mechanisms of tumor development in patients affected with RET germline mutations remain unknown. In vitro studies have certain pitfalls, one of which is the use of cell culture systems such as the NIH3T3 cells, in which RET usually is not expressed in contrast to the in vivo situation. Recent data suggest that an overrepresentation of mutant RET as a second hit event might trigger tumorigenesis. However, alterations in other genes might contribute to this overrepresentation of RET or impact on MEN 2-related tumor development through completely different mechanisms and pathways. The final goal of further elucidating the natural history and pathogenesis of MEN2-related tumors should be the chance to offer patients with RET germline mutations an optimal cancer prevention (e.g. codon specific recommendations for prophylactic thyroidectomy) and treatment program, especially for metastatic medullary thyroid carcinoma for which presently no effective therapy other than surgery exists.     

Molecular genetics of pediatric central nervous system tumors

Recent advances in molecular biology have enhanced our understanding of the pathogenesis of brain tumors, particularly in children. The use of molecular diagnostic tools is quickly becoming a standard component in the diagnosis and classification of brain tumors in children, in addition to providing insight leading to treatment stratification and improved outcome prediction. All new protocols involving treatments for brain tumors in children include studies of biomarkers and biologic correlates as a means to identify new targets for therapeutics and possible intervention strategies.     

Expression and role of cadherins in astrocytic tumors

Cadherins are Ca²⁺-dependent cell adhesion molecules that play an important role in tissue formation and morphogenesis in multicellular organisms. In recent years, there have been reports of cadherin involvement in tumor invasion and metastasis. Twenty-two surgical specimens and some cultured cells were studied by immunohistochemical staining. No significant difference was observed in the patients with anaplastic astrocytoma, whereas decreased expression of N-cadherin was detected at the time of recurrence in those with glioblastoma. In these groups, cerebrospinal fluid dissemination was found, and contralateral cerebral metastases and extracranial metastases were observed. We conclude that decreased N-cadherin expression at the immunohistochemically demonstrated time of recurrence correlates with tumor invasion and dissemination of cerebrospinal fluid.     

Molecular profiling of pediatric brain tumors: Insight into biology and treatment

Recent history has witnessed unparalleled advances in our understanding of tumor biology, owing in large part to the publication of the human genome project. Paired with improvements in microarray technologies, the combination of genetic and expression profiles provides a unique opportunity to further enhance our understanding of the underlying mechanisms that drive tumor growth. Thus, integrated analysis of identified molecular changes with clinical and histologic data may further delineate a new risk stratification system for pediatric brain tumors, allowing more patient-tailored therapy and molecular-based therapeutic interventions.     

Progression as exemplified by human astrocytic tumors.

The last 10 years has seen major improvements in our understanding of the genetic anomalies that lie behind the development and progression of human astrocytic tumors. The least aggressive astrocytomas frequently show loss of wild type p53 as well as losses of alleles from a number of regions of the genome. The genes targeted have yet to be identified. The most aggressive tumors, the glioblastomas, show mutations affecting the cellular mechanisms controlling entry into the S-phase of the cell cycle. The picture has become more complex as regards the mechanisms targeted. The heterogeneous genetic abnormalities reported previously in individual tumors of the same type have become easier to understand with the realization that they represent the mutation of different genes that code for components of the same cellular control mechanisms. There remain many routes to explore before we understand in detail the molecular mechanisms behind the phenotype of these tumors.     

Nestin expression in astrocytic tumors delineates tumor infiltration

Nestin is an intermediate filament protein expressed in undifferentiated cells during central nervous system development, and glioma is known to be a highly infiltrative tumor. We determined whether nestin was expressed in astrocytic tumors and could identify infiltrating tumor cells. We screened 65 archival, paraffin-embedded adult astrocytic tumors using immunohistochemical staining and computerized overlaid photographs. Normal biopsied brains and metastatic brain tumors were also examined. The intensity of nestin expression corresponded to the tumor grade. All 33 glioblastoma cases showed positive and extensive staining, which was less positive in diffuse astrocytoma. Overlaid images showed that nestin immunostaining delineated tumor invasion into adjacent gray and white matter. Nestin is a useful marker for examining the infiltration of malignant cells into surrounding tissue.     

Molecular pathogenesis of ovarian borderline tumors: new insights and old challenges.

Ovarian borderline (low malignant potential) tumors are a puzzling group of neoplasms that do not fall neatly into benign or malignant categories. Their behavior is enigmatic, their pathogenesis unclear, and their clinical management controversial, especially for serous borderline tumors (SBT), the most common type of ovarian borderline tumor. Clarifying the nature of borderline tumors and their relationship to invasive carcinoma has puzzled investigators since the category was created over 30 years ago. Much of the confusion and controversy concerning these tumors is due to a lack of understanding of their pathogenesis and an absence of a model for the development of ovarian carcinoma. This review summarizes recent molecular studies of ovarian borderline tumors with special emphasis on the role of SBT in tumor progression and its relationship to ovarian serous carcinoma.     

Biological role of thymidine phosphorylase in human astrocytic tumors

Thymidine phosphorylase (TP) has strong angiogenic activity and is overexpressed in a wide variety of malignant tumors. To elucidate the role of TP in human astrocytic tumors, we immunohistochemically investigated the expression of TP in 62 astrocytic tumors (12 astrocytomas, 12 anaplastic astrocytomas and 38 glioblastomas). Fifty-five astrocytic tumors (88.7%) were immunopositive for TP. The level of TP-expression was significantly correlated with the malignancy grade of astrocytic tumors; most of malignant gliomas highly expressed TP, while a small number of cells were positive in low grade astrocytomas (p < 0.001). Using double-immunostaining, we clarified that TP-expression was predominantly detectable in macrophages. There was no significant correlation between MIB-1 labeling index and TP-expression. However, TP-expression and the microvessel density were well correlated. These suggest that TP, mainly produced by the infiltrated macrophages, may play an important role in the progression of astrocytic tumors via neovascularization. Inhibitor of TP may represent a therapeutic modality for treating malignant gliomas.     

脑星形细胞瘤弥散张量成像的初步研究

背景与目的:弥散张量成像(diffusiontensorimaging,DTI)是一种高级的、定量的弥散加权成像形式,它不仅可以计算每一体素内水分子弥散的显著弥散系数(apparentdiffusioncoefficient,ADC),而且可以计算出弥散的各向异性指数。国外对脑肿瘤的研究多采用弥散加权成像,本研究采用DTI方法检测脑内星形细胞瘤患者的肿瘤实质组织、瘤内囊变坏死区、瘤周水肿与正常脑组织中ADC、部分各向异性指数(fractionalanisotropy,FA)及相对各向异性指数(relativeanisotropy,RA)值,及上述指标在星形细胞瘤分级中的价值。方法:对确诊的14例脑星形细胞瘤(1～2级10例,3～4级4例)进行DTI。测定不同组织中ADC、FA及RA值。结果:将14例脑星形细胞瘤作为一组分析时,增强的肿瘤实质组织犤(1.14±0.13)×10-3mm2/s犦、瘤内囊变坏死区犤(2.04±0.50)×10-3mm2/s犦及瘤周水肿组织犤(1.55±0.19)×10-3mm2/s犦的ADC值同正常脑组织犤(0.74±0.08)×10-3mm2/s犦相比均有显著性差异(P<0.05)。肿瘤实性部分的ADC值犤增强区域:(1.14±0.13)×10-3mm2/s,非增强区域:(1.01±0.25)×10-3mm2/s犦同瘤内囊变坏死区、瘤周水肿组织区比较均有显著性差异(P<0.05)。增强的肿瘤实质组织(FA:0.21±0.08,RA:0.23±0.07)、瘤内囊变坏死区(FA:0.14±0.06,RA:0     

Cytogenetic abnormalities related to histopathologic grade of astrocytic tumors

Cytogenetic analysis was performed on 7 lowgrade astrocytomas, 10 anaplastic astrocytomas, and 14 glioblastomas. Abnormal chromosome numbers were noted in all cases of high-grade astrocytomas but were rarely noted in low-grade astrocytomas (28%). The most consistent changes in high-grade astrocytomas were complete loss of chromosome 10 (61%), gain of chromosome 7 (56%), and loss of chromosome 17 (28%). Certain structural abnormalities, such as marker chromosomes and double minutes (33%), and the deletion and translocation of chromosomes 1 (33%) and 17 (17%), were also noted. These results indicate that changes in the number and/or structure of chromosomes with related inactivation of tumor suppressor gene or oncogene activation might play a critical role in the formation and anaplastic progression of astrocytic tumors.     

人脑星形细胞肿瘤组织中Survivin基因表达的研究

目的:探讨Survivin mRNA的表达与星形细胞肿瘤发生、发展的关系。方法:应用RT-PCR技术检测各级别星形细胞肿瘤组织及非肿瘤(脑)组织中Survivin mRNA的表达水平。结果:Survivin mRNA在肿瘤组织和非肿瘤(脑)组织中的表达阳性率分别为68.6%和8.3%;Survivin mRNA的相对含量在肿瘤组织和非肿瘤(脑)组织中分别为119.67±46.56和13.19±9.26;Survivin在肿瘤组织中的表达显著高于其在非肿瘤(脑)组织中的表达,P=0.000。结论:Survivin mRNA表达与星形细胞肿瘤的发生、发展呈显著正相关,是评估星形细胞肿瘤恶性生物学行为的可靠指标;Survivin作为凋亡抑制基因为星形细胞肿瘤的治疗提供了一个新靶点。