The molecular landscape of diffuse glioma and prospects for biomarker development

Malignant Intracranial High Grade Glioma and Current Treatment Strategy

Malignant high-grade glioma (HGG) is the most common and extremely fatal type of primary intracranial tumor. These tumors recurred within 2 to 3 cm of the primary region of tumor resection in the majority of cases. Furthermore, the blood-brain barrier significantly limited the access of many systemically administered chemotherapeutics to the tumor, pointing towards a stringent need for new therapeutic patterns. Therefore, targeting therapy using local drug delivery for HGG becomes a priority for the development of novel therapeutic strategies. The main objectives to the effective use of chemotherapy for HGG include the drug delivery to the tumor region and the infusion of chemotherapeutic agents into the vascular supply of a tumor directly, which could improve the pharmacokinetic profile by enhancing drug delivery to the neoplasm tissue. Herein, we reviewed clinical and molecular features, different methods of chemotherapy application in HGGs, especially the existing and promising targeting therapies using local drug delivery for HGG which could effectively inhibit tumor invasion, proliferation and recurrence of HGG to combat the deadly disease. Undoubtedly, novel chemical medicines targeting these HGG may represent one of the most important directions in the Neuro-oncology.

Novel insights into the epigenetics of diffuse glioma

Loss-of-function mutations of the chromatin regulator ATRX (α-thalassemia mental retardation X-linked) occur frequently in diffuse gliomas, but the molecular mechanisms by which ATRX inactivation promotes oncogenesis remain unclear. We recently reported that Atrx deficiency drives glioma-relevant phenotypes, such as increased motility and astrocytic differentiation profiles, by directly modulating epigenomic lanscapes in glioma cells of origin. Our work has significant implications on the role of epigenetic regulator dysfunction in the oncogenic process.

Establishing a Robust Molecular Taxonomy for Diffuse Gliomas of Adulthood

The comprehensive molecular profiling of cancer has dramatically altered conceptions of numerous tumor types, particularly with regard to their fundamental classification. In the case of primary brain tumors, the widespread use of disease-defining biomarker sets is profoundly reshaping existing diagnostic entities that had been designated solely by histopathological criteria for decades. This review describes recent progress for diffusely infiltrating gliomas of adulthood, the most common primary brain tumor variants. More specifically, it details how routine incorporation of a handful of highly prevalent molecular alterations robustly designates refined subclasses of glioma that transcend conventional histopathological designations.

miR-146b-5p functions as a tumor suppressor by targeting TRAF6 and predicts the prognosis of human gliomas

Down-regulation of miR-146b-5p contributes to tumorigenesis in several human cancers. However, the relevance of miR-146b-5p to prognosis, proliferation and apoptosis in gliomas remains unknown. In the present study, we demonstrated that miR-146b-5p expression was inversely correlated with grades and Ki-67 index in 147 human glioma specimens, but positively correlated with patients’ survival. Furthermore, two distinct subgroups of patients with grade I-IV gliomas with different prognoses were identified according to miR-146b-5p expression in our specimens. Cox regression showed that miR-146b-5p was an independent predictor for patients’ survival. Overexpression of miR-146b-5p dramatically suppressed glioma cell proliferation and induced apoptosis. Mechanistically, we validated TRAF6 as a direct functional target of miR-146b-5p and found that miR-146b-5p overexpression significantly decreased phosphorylated TAK1 and IκBα, the pivotal downstream effectors of TRAF6. Moreover, TRAF6 expression was positively correlated with glioma grades and Ki-67 index but inversely correlated with miR-146b-5p expression and predicted poor prognosis of glioma patients. In glioblastoma cell lines, silencing of TRAF6 could mimic the anti-tumor effect of miR-146b-5p. Our findings identify miR-146b-5p as a tumor suppressor and novel prognostic biomarker of gliomas, and suggest miR-146b-5p and TRAF6 as potential therapeutic candidates for malignant gliomas.

Clinical ramifications of "genomic staging" of low-grade gliomas

"Low-grade gliomas" (LGGs), classification of which is derived from histopathological observations, exhibit significant heterogeneity in clinical behavior. Recently, increasing attention has been paid to genomic analyses of these tumors, to aid in treatment and prognostic decision-making. We discuss herein the recent genomic analysis of gliomas from two major recent publications, and also the results of seminal LGG trials in the context of molecular and genomic stratification, with respect to both prognosis and response to therapy. We also analyze implications of these "molecular classifications". We propose separating out the worst prognostic subsets, whose outcomes resemble those of glioblastoma patients. Lastly, a brief discussion is provided regarding translating this collective knowledge into the clinic and in treatment decisions; also addressed are some of the many questions that still need to be examined in light of these strong and emerging data.

The evolving molecular genetics of low-grade glioma

Low-grade gliomas (LGG) constitute grades I and II tumors of astrocytic and grade II tumors of oligodendroglial lineage. Although these tumors are typically slow growing, they may be associated with significant morbidity and mortality because of recurrence and malignant progression, even in the setting of optimal resection. LGG in pediatric and adult age groups are currently classified by morphologic criteria. Recent years have heralded a molecular revolution in understanding brain tumors, including LGG. Next-generation sequencing has definitively demonstrated that pediatric and adult LGG fundamentally differ in their underlying molecular characteristics, despite being histologically similar. Pediatric LGG show alterations in FGFR1 and BRAF in pilocytic astrocytomas and FGFR1 alterations in diffuse astrocytomas, each converging on the mitogen-activated protein kinase signaling pathway. Adult LGG are characterized by IDH1/2 mutations and ATRX mutations in astrocytic tumors and IDH1/2 mutations and 1p/19q codeletions in oligodendroglial tumors. TERT promoter mutations are also noted in LGG and are mainly associated with oligodendrogliomas. These findings have considerably refined approaches to classifying these tumors. Moreover, many of the molecular alterations identified in LGG directly impact on prognosis, tumor biology, and the development of novel therapies.

Trends in central nervous system tumor incidence relative to other common cancers in adults, adolescents, and children in the United States, 2000 to 2010

BACKGROUND

Time trends in cancer incidence rates (IR) are important to measure the changing burden of cancer on a population over time. The overall IR of cancer in the United States is declining. Although central nervous system tumors (CNST) are rare, they contribute disproportionately to mortality and morbidity. In this analysis, the authors examined trends in the incidence of the most common cancers and CNST between 2000 and 2010.

METHODS

The current analysis used data from the United States Cancer Statistics publication and the Central Brain Tumor Registry of the United States. Age-adjusted IR per 100,000 population with 95% confidence intervals and the annual percent change (APC) with 95% confidence intervals were calculated for selected common cancers and CNST overall and by age, sex, race/ethnicity, selected histologies, and malignancy status.

RESULTS

In adults, there were significant decreases in colon (2000-2010: APC, -3.1), breast (2000-2010: APC, -0.8), lung (2000-2010: APC, -1.1), and prostate (2000-2010: APC, -2.4) cancer as well as malignant CNST (2008-2010: APC, -3.1), but a significant increase was noted in nonmalignant CNST (2004-2010: APC, 2.7). In adolescents, there were significant increases in malignant CNST (2000-2008: APC, 1.0) and nonmalignant CNST (2004-2010: APC, 3.9). In children, there were significant increases in acute lymphocytic leukemia (2000-2010: APC, 1.0), non-Hodgkin lymphoma (2000-2010: APC, 0.6), and malignant CNST (2000-2010: APC, 0.6).

CONCLUSIONS

Surveillance of IR trends is an important way to measure the changing public health and economic burden of cancer. In the current study, there were significant decreases noted in the incidence of adult cancer, whereas adolescent and childhood cancer IR were either stable or increasing.