Age-related differences in 1p and 19q deletions in oligodendrogliomas

Evidence for age-related contributions of DNA damage and epigenetics in brain tumorigenesis

Glioblastoma (GBM) is a highly malignant primary brain tumour displaying rapid cell proliferation and infiltration. GBM primarily occurs at older age; however, younger populations have also been affected. In GBM and other cancers, genetic and epigenetic alterations promote tumorigenesis causing increased cell proliferation and invasiveness. This investigation explored epigenetic events as contributing factors, especially in gliomas that arise in patients aged 40-60 years. Furthermore, DNA damage in tumours with respect to age was assessed. Archival fixed tissues from 88 cases of glioblastoma and adjacent non-malignant tissues were tested. Global methylation and DNA damage were measured using ELISA detection of 5-methyl cytosine and 8-hydroxy guanine, respectively. IDH mutations and CDKN2 promoter hypermethylation were analysed by pyrosequencing. Tumour tissue was hypomethylated compared with non-malignant tissue (P = .001), and there was a trend towards increased methylation with increasing age. There was a significant increase in DNA damage in patients older than forty years compared with those aged forty years or younger (P = .035). CDKN2 promoter methylation levels followed the age trends of global methylation in this patient group. Patients younger than 60 had more frequently mutated IDH (P = .004). Conclusions: The data support the potential of epigenetic factors in promoting tumorigenesis in younger patients, while increased DNA damage contributes to tumorigenesis in the older patients.

Exploiting molecular biology for diagnosis and targeted management of pediatric low-grade gliomas

The majority of brain tumors arising in children are low-grade gliomas. Although historically categorized together as pediatric low-grade gliomas (PLGGs), there is significant histologic and genetic diversity within this group. In general, prognosis for PLGGs is excellent, and limitation of sequelae from tumor and treatment is paramount. Advances in high-throughput genetic sequencing and gene expression profiling are fundamentally changing the way PLGGs are classified and managed. Here, we review the histologic subtypes and highlight how recent advances in elucidating the molecular pathogenesis of these tumors have refined diagnosis and prognostication. Additionally, we discuss how characterizing specific genetic alterations has paved the way for the rational use of targeted therapies that are currently in various phase clinical trials.

The molecular biology of WHO grade II gliomas

The WHO grading scheme for glial neoplasms assigns Grade II to 5 distinct tumors of astrocytic or oligodendroglial lineage: diffuse astrocytoma, oligodendroglioma, oligoastrocytoma, pleomorphic xanthoastrocytoma, and pilomyxoid astrocytoma. Although commonly referred to collectively as among the "low-grade gliomas," these 5 tumors represent molecularly and clinically unique entities. Each is the subject of active basic research aimed at developing a more complete understanding of its molecular biology, and the pace of such research continues to accelerate. Additionally, because managing and predicting the course of these tumors has historically proven challenging, translational research regarding Grade II gliomas continues in the hopes of identifying novel molecular features that can better inform diagnostic, prognostic, and therapeutic strategies. Unfortunately, the basic and translational literature regarding the molecular biology of WHO Grade II gliomas remains nebulous. The authors' goal for this review was to present a comprehensive discussion of current knowledge regarding the molecular characteristics of these 5 WHO Grade II tumors on the chromosomal, genomic, and epigenomic levels. Additionally, they discuss the emerging evidence suggesting molecular differences between adult and pediatric Grade II gliomas. Finally, they present an overview of current strategies for using molecular data to classify low-grade gliomas into clinically relevant categories based on tumor biology.

Clinical significance of chromosome 1p/19q loss of heterozygosity and Sox17 expression in oligodendrogliomas

OBJECTIVE

To study chromosome 1p/19q loss of heterozygosity (LOH) and Sox17 protein expression in oligodendrogliomas and correlate this loss with clinicopathological features.

METHODS

This study included 100 cases of oligodendrogliomas at the First Affiliated Hospital of Xinjiang Medical University from 2003 to 2014. The cases included paraffin-embedded tissues from 50 low-grade oligodendrogliomas and 50 anaplastic oligodendrogliomas. Chromosome 1p/19q LOH was detected by fluorescence in situ hybridization (FISH) and Sox17 protein expression was analyzed by immunohistochemistry. Clinicopathological characteristics of the oligodendrogliomas were compared and prognosis analyzed using Cox regression and Kaplan-Meier analyses.

RESULTS

The LOH positivity rate of 1p/19q was 52% in 50 cases of low-grade oligodendrogliomas and 68% in 50 cases of anaplastic oligodendrogliomas (P = 0.102). The rates of Sox17 expression were significantly different in oligodendrogliomas (82%) and anaplastic oligodendrogliomas (62%, P = 0.026). Single factor analysis determined that 1p/19q LOH (P = 0.000), Sox17 protein expression (P = 0.000), location (P = 0.001), chemotherapy (P = 0.000), and radiation therapy (P = 0.001) were associated with oligodendroglioma patient prognosis. Cox multiple factors regression analysis determined that 1p/19q LOH and Sox17 expression were independent prognostic factors of oligodendrogliomas.

CONCLUSION

In this study, oligodendroglioma patients with 1p/19q LOH and Sox17 protein expression had a better prognosis. Thus, analysis of 1p/19q LOH and Sox17 protein expression could significantly enhance diagnostic accuracy, guide treatment, and improve the prognosis.

Clinicopathologic features of pediatric oligodendrogliomas: a series of 50 patients

Oligodendrogliomas are an important adult form of diffuse gliomas with a distinctive clinical and genetic profile. Histologically similar tumors occurring rarely in children are incompletely characterized. We studied 50 patients with oligodendrogliomas (median age at diagnosis 8 y, range 7 mo to 20 y). Tumors resembling dysembryoplastic neuroepithelial tumors or pilocytic astrocytomas or those having a "mixed" histology were excluded. Tumors at first diagnosis were low grade (n=38) or anaplastic (n=12). Histologic features included uniform round cells with perinuclear halos (100%), secondary structures (predominantly perineuronal satellitosis) (90%), calcifications (46%), and microcysts (44%). Sequential surgical specimens were obtained in 8 low-grade oligodendroglioma patients, with only 1 progressing to anaplasia. Studies for 1p19q performed in 40 cases demonstrated intact 1p19q loci in 29 (73%), 1p19q codeletion in 10 (25%), and 1p deletion with intact 19q in 1 (2%). Except for 2 young patients (3 and 11 y of age), patients with 1p19q codeletion were older than 16 years at diagnosis. Mutant IDH1 (R132H) protein immunohistochemistry was positive in 4 (of 22) (18%) cases, 3 of which also had 1p19q codeletion, whereas 1p19q status was not available on the fourth case. There was a nonsignificant trend for worse overall survival in grade III tumors, but no significant association with age, extent of resection, or 1p19q status. In summary, oligodendrogliomas with classic histology occur in the pediatric population but lack 1p19q codeletion and IDH1 (R132H) mutations in most instances. They are predominantly low grade, recur/clinically progress in a subset, but demonstrate a relatively low frequency of histologic progression.

Homozygous deletion of TNFRSF4, TP73, PPAP2B and DPYD at 1p and PDCD5 at 19q identified by multiplex ligation-dependent probe amplification (MLPA) analysis in pediatric anaplastic glioma with questionable oligodendroglial component

Background

Pediatric oligodendrogliomas are rare and appear to show a different molecular profile from adult tumors. Some gliomas display allelic losses at 1p/19q in pediatric patients, although less frequently than in adult patients, but this is rare in tumors with an oligodendroglial component. The molecular basis of this genomic abnormality is unknown in pediatric gliomas, but it represents a relatively common finding in pediatric oligodendroglioma-like neoplasms with leptomeningeal dissemination.

Results

Multiplex ligation-dependent probe amplification (MLPA) analysis using SALSA P088-B1 for the analysis of the 1p/19q allelic constitution in a pediatric anaplastic (oligodendro)-glioma showed homozygous co-deletion for markers: TNFRSF4 (located at 1p36.33), TP73 (1p36.32), PPAP2B (1pter-p22.1), DPYD (1p21.3), and PDCD5 (19q13.12), and hemizygous deletion of BAX (19q13.3-q13.4). No sequence changes for R132 and R172 of the IDH1/2 genes were identified.

Conclusions

The molecular findings in this pediatric anaplastic glioma do not allow for a clearly definitive pathological diagnosis. However, the findings provide data on a number of 1p/19q genomic regions that, because of homozygotic deletion, might be the location of genes that are important for the development and clinical evolution of some malignant gliomas in children.

Molecular profile of oligodendrogliomas in young patients

Several studies on molecular profiling of oligodendrogliomas (OGs) in adults have shown a distinctive genetic pattern characterized by combined deletions of chromosome arms 1p and 19q, O6-methylguanine-methyltransferase (MGMT) methylation, and isocitrate dehydrogenase 1 (IDH1) mutation, which have potential diagnostic, prognostic, and even therapeutic relevance. OGs in pediatric and young adult patients are rare and have been poorly characterized on a molecular and biological basis, and it remains uncertain whether markers with prognostic significance in adults also have predictive value in these patients. Fourteen cases of OGs in young patients (age, ≤ 25 years) who received a diagnosis over 7 years were selected (7 pediatric patients age ≤ 18 years and 7 young adults aged 19-25 years). The cases were evaluated for 1p/19q status, MGMT promoter methylation, p53 mutation, and IDH1 mutation. None of the pediatric cases showed 1p/19q deletion. In young adults, combined 1p/19q loss was observed in 57% and isolated 1p loss in 14% of cases. The majority of cases in both subgroups (71% in each) harbored MGMT gene promoter methylation. TP53 and IDH1 mutations were not seen in any of the cases in both the groups. To our knowledge, this is the first study to show that molecular profile of OGs in pediatric and young adult patients is distinct. Further large-scale studies are required to identify additional clinically relevant genetic alterations in this group of patients.

Genomic stability prevails in North-African hepatocellular carcinomas

The molecular pathogenesis of hepatocellular carcinoma, a tumour characterized by a vast clinical heterogeneity, remains unexplored outside Europe and Eastern Asia. We analysed by direct sequencing or loss of heterozygosity assay, the common targets of genomic alterations in 42 hepatocellular carcinomas collected in western North-Africa. Overall, genomic instability was uncommon, allelic losses affecting mostly chromosomes 1p, 4q, 8p and 17p (24-28% of cases). CTNNB1 and TP53 were infrequently mutated (9 and 17% of cases, respectively). Surprisingly, TP53 mutation R249S, diagnostic of aflatoxin B1 exposure, usually frequent in Africa, was exceptional (one case), indicating that in western North-Africa, hepatocellular carcinoma genetics differs markedly from that of the remainder of the continent.

Molecular genetic evidence supporting a novel human hepatocellular carcinoma tumor suppressor locus at 13q12.11

A novel 1-cM (1.8 Mb) homozygous deletion (HD) on 13q12.11 was identified in a human hepatocellular carcinoma (HCC) cell line, SK-Hep-1, after high-density genetic marker scan and Southern blotting analysis. A loss of heterozygosity (LOH) analysis indicated that LOH frequency of the HD region in 48 pairs of HCC tissues was 52%. Interestingly, the occurrence of LOH in the 13q12.11 HD region is significantly associated with early-onset HCC, inferred from Fisher's exact test (P = 0.0047) and Mann-Whitney test (P = 0.023). Since the novel 1-cM (1.8 Mb) HD region is gene-rich with more than 37 predicted transcripts, we used a candidate gene approach by examining down-regulation of known tumor suppressor genes (TSGs), including LATS2, TG737, CRYL1, and GJB2, in HCC tissues. We detected only 14% down-regulation of the LAST2 gene that flanks the outside of the HD, in HCC tissues, by quantitative RT-PCR assays. However, we observed significant down-regulation of the TG737, CRYL1, and GJB2 genes located within the HD in 59, 64, and 71% of HCC tissues, respectively. Together, our results indicated that the identified 13q12.11 HD region contained at least three significant down-regulated TSGs, and preferential LOH in early-onset HCC patients is a putative tumor suppressor locus in HCC.