Magnetic resonance imaging characteristics of glioblastoma multiforme: implications for understanding glioma ontogeny

Reprogramming Glioblastoma Cells into Non-Cancerous Neuronal Cells as a Novel Anti-Cancer Strategy

Glioblastoma Multiforme (GBM) is an aggressive brain tumor with a high mortality rate. Direct reprogramming of glial cells to different cell lineages, such as induced neural stem cells (iNSCs) and induced neurons (iNeurons), provides genetic tools to manipulate a cell's fate as a potential therapy for neurological diseases. NeuroD1 (ND1) is a master transcriptional factor for neurogenesis and it promotes neuronal differentiation. In the present study, we tested the hypothesis that the expression of ND1 in GBM cells can force them to differentiate toward post-mitotic neurons and halt GBM tumor progression. In cultured human GBM cell lines, including LN229, U87, and U373 as temozolomide (TMZ)-sensitive and T98G as TMZ-resistant cells, the neuronal lineage conversion was induced by an adeno-associated virus (AAV) package carrying ND1. Twenty-one days after AAV-ND1 transduction, ND1-expressing cells displayed neuronal markers MAP2, TUJ1, and NeuN. The ND1-induced transdifferentiation was regulated by Wnt signaling and markedly enhanced under a hypoxic condition (2% O2 vs. 21% O2). ND1-expressing GBM cultures had fewer BrdU-positive proliferating cells compared to vector control cultures. Increased cell death was visualized by TUNEL staining, and reduced migrative activity was demonstrated in the wound-healing test after ND1 reprogramming in both TMZ-sensitive and -resistant GBM cells. In a striking contrast to cancer cells, converted cells expressed the anti-tumor gene p53. In an orthotopical GBM mouse model, AAV-ND1-reprogrammed U373 cells were transplanted into the fornix of the cyclosporine-immunocompromised C57BL/6 mouse brain. Compared to control GBM cell-formed tumors, cells from ND1-reprogrammed cultures formed smaller tumors and expressed neuronal markers such as TUJ1 in the brain. Thus, reprogramming using a single-factor ND1 overcame drug resistance, converting malignant cells of heterogeneous GBM cells to normal neuron-like cells in vitro and in vivo. These novel observations warrant further research using patient-derived GBM cells and patient-derived xenograft (PDX) models as a potentially effective treatment for a deadly brain cancer and likely other astrocytoma tumors.

Time-to-event overall survival prediction in glioblastoma multiforme patients using magnetic resonance imaging radiomics

PURPOSE

Glioblastoma Multiforme (GBM) represents the predominant aggressive primary tumor of the brain with short overall survival (OS) time. We aim to assess the potential of radiomic features in predicting the time-to-event OS of patients with GBM using machine learning (ML) algorithms.

MATERIALS AND METHODS

One hundred nineteen patients with GBM, who had T1-weighted contrast-enhanced and T2-FLAIR MRI sequences, along with clinical data and survival time, were enrolled. Image preprocessing methods included 64 bin discretization, Laplacian of Gaussian (LOG) filters with three Sigma values and eight variations of Wavelet Transform. Images were then segmented, followed by the extraction of 1212 radiomic features. Seven feature selection (FS) methods and six time-to-event ML algorithms were utilized. The combination of preprocessing, FS, and ML algorithms (12 × 7 × 6 = 504 models) was evaluated by multivariate analysis.

RESULTS

Our multivariate analysis showed that the best prognostic FS/ML combinations are the Mutual Information (MI)/Cox Boost, MI/Generalized Linear Model Boosting (GLMB) and MI/Generalized Linear Model Network (GLMN), all of which were done via the LOG (Sigma = 1 mm) preprocessing method (C-index = 0.77). The LOG filter with Sigma = 1 mm preprocessing method, MI, GLMB and GLMN achieved significantly higher C-indices than other preprocessing, FS, and ML methods (all p values < 0.05, mean C-indices of 0.65, 0.70, and 0.64, respectively).

CONCLUSION

ML algorithms are capable of predicting the time-to-event OS of patients using MRI-based radiomic and clinical features. MRI-based radiomics analysis in combination with clinical variables might appear promising in assisting clinicians in the survival prediction of patients with GBM. Further research is needed to establish the applicability of radiomics in the management of GBM in the clinic.

Regional Development of Glioblastoma: The Anatomical Conundrum of Cancer Biology and Its Surgical Implication

Glioblastoma (GBM) are among the most common malignant central nervous system (CNS) cancers, they are relatively rare. This evidence suggests that the CNS microenvironment is naturally equipped to control proliferative cells, although, rarely, failure of this system can lead to cancer development. Moreover, the adult CNS is innately non-permissive to glioma cell invasion. Thus, glioma etiology remains largely unknown. In this review, we analyze the anatomical and biological basis of gliomagenesis considering neural stem cells, the spatiotemporal diversity of astrocytes, microglia, neurons and glutamate transporters, extracellular matrix and the peritumoral environment. The precise understanding of subpopulations constituting GBM, particularly astrocytes, is not limited to glioma stem cells (GSC) and could help in the understanding of tumor pathophysiology. The anatomical fingerprint is essential for non-invasive assessment of patients’ prognosis and correct surgical/radiotherapy planning.

Safety analysis and complications of condylar screws in a single-surgeon series of 250 occipitocervical fusions

Objective

Condylar screw fixation is a rescue technique and an alternative to the conventional configuration of occipitocervical fusion. Condylar screws are utilized when previous surgical bone removal along the supraocciput has occurred which makes anchoring of a traditional barplate technically difficult or impossible. However, the challenging dissection of C0-1 necessary for condylar screw fixation and the concerns about possible complications have, thus far, prevented the acquisition of large surgical series utilizing occipital condylar screws. In the largest case series to date, this paper aims to evaluate the safety profile and complications of condylar screw fixation for occipitocervical fusion.

Methods

A retrospective safety and complication-based analysis of occipitocervical fusion via condylar screws fixation was performed.

Results

A total of 250 patients underwent occipitocervical fusions using 500 condylar screws between September 2012 and September 2018. No condylar screw pullouts, or vertebral artery impingements were observed in this series. The sacrifice of condylar veins during the dissection at C0-1 did not cause any venous stroke. Hypotrophic condyles were found in 36.4% (91 of the 250) cases and did not prevent the insertion of condylar screws. Two transient hypoglossal deficits occurred at the beginning of this surgical series and were followed by recovery a few months later. Corrective strategies were effective in preventing further hypoglossal injuries.

Conclusions

This surgical series suggests that the use of condylar screws fixation is a relatively safe and reliable option for OC fusion in both adult and pediatric patients. Methodical dissection of anatomical landmarks, intraoperative imaging, and neurophysiologic monitoring allowed the safe execution of the largest series of condylar screws reported to date. Separate contributions will follow in the future to provide details about the long-term clinical outcome of this series.

Rates and patterns of clonal oncogenic mutations in the normal human brain

While oncogenic mutations have been found in non-diseased, proliferative non-neural tissues, their prevalence in the human brain is unknown. Targeted sequencing of genes implicated in brain tumors in 418 samples derived from 110 individuals of varying ages, without tumor diagnoses, detected oncogenic somatic single-nucleotide variants (sSNVs) in 5.4% of the brains, including IDH1 R132H. These mutations were largely present in subcortical white matter and enriched in glial cells, and surprisingly, were less common in older individuals. A depletion of high-allele frequency sSNVs representing macroscopic clones with age was replicated by analysis of bulk RNAseq data from 1,816 non-diseased brain samples ranging from fetal to old age. We also describe large clonal copy number variants, and that sSNVs show mutational signatures resembling those found in gliomas, suggesting that mutational processes of the normal brain drive early glial oncogenesis. This study helps understand the origin and early evolution of brain tumors.

The Promoting Effect of Traumatic Brain Injury on the Incidence and Progression of Glioma: A Review of Clinical and Experimental Research

The role of traumatic brain injury in the development of glioma is highly controversial since first presented. This is not unexpected because traumatic brain injuries are overwhelmingly more common than glioma. However, the causes of post-traumatic glioma have been long discussed and still warrant further research. In this review, we have presented an overview of previous cohort studies and case–control studies. We have summarized the roles of microglial cells, macrophages, astrocytes, and stem cells in post-traumatic glioma formation and development, and reviewed various carcinogenic factors involved during traumatic brain injury, especially those reported in experimental studies indicating a relationship with glioma progression. Besides, traumatic brain injury and glioma share several common pathways, including inflammation and oxidative stress; however, the exact mechanism underlying this co-occurrence is yet to be discovered. In this review, we have summarized current epidemiological studies, clinical reports, pathophysiological research, as well as investigations evaluating the probable causes of co-occurrence and treatment possibilities. More efforts should be directed toward elucidating the relationship between traumatic brain injury and glioma, which could likely lead to promising pharmacological interventions towards designing therapeutic strategies.

Subventricular zone contacting glioblastoma: tumor size, molecular biological factors and patient survival

BACKGROUND

Several studies show that subventricular zone (SVZ) contact of glioblastoma at diagnosis is a negative prognosticator of survival. In this report, we study glioblastoma patient survival, molecular biological and MRI-based volumetric findings according to SVZ contact.

PATIENTS AND METHODS

We conducted a retrospective study of adult patients diagnosed with supratentorial glioblastoma and uniformly treated with temozolomide-based chemoradiotherapy after surgery. The patient cohort was dichotomized according to tumor contact with the SVZ at diagnosis as determined on preoperative MR imaging. Tumor volume was measured using semi-automated segmentation technique. MGMT-gene promoter methylation and IDH mutation status were determined on stored tumor tissue. Kaplan-Meier survival curves were constructed. Cox regression analysis was used to adjust for known confounding factors of glioblastoma patient survival.

RESULTS

A total of 214 patients were included in the study of whom 68% belonged to the SVZ_pos group. Median tumor volume was significantly larger in the SVZ_pos group (33,8 mL vs 15,6 mL; p < .001). MGMT-unmethylated glioblastoma was more frequent in the SVZ_pos group (61.4% vs 44.9%; p = .028). The overall survival and progression-free survival were 12.2 months and 5.9 months for the SVZ_pos patient group but 16.9 months and 10.3 months for the SVZ_neg group (log-rank p = .016 and .007 respectively). In multivariate Cox survival analysis, SVZ contact proved a negative prognostic parameter, independent from age, KPS, extent of resection, MGMT-methylation and IDH mutation status.

CONCLUSIONS

This study confirms SVZ contact at diagnosis as an independent negative prognostic factor for glioblastoma patient survival. SVZ_pos glioblastoma had larger tumor size and a larger proportion of unmethylated tumors than SVZ_neg glioblastoma. Further research is needed to establish whether the observed differences are solely explained by a different molecular profile of SVZ_pos glioblastoma or by interaction of glioblastoma with the unique SVZ microenvironment.

The Role of the T2-FLAIR Mismatch Sign as an Imaging Marker of IDH Status in a Mixed Population of Low- and High-Grade Gliomas

Our study evaluated the role of the T2-fluid-attenuated inversion recovery (FLAIR) mismatch sign in detecting isocitrate dehydrogenase (IDH) mutations based on a mixed sample of 24 patients with low- and high- grade gliomas. The association between the two was realized using univariate and multivariate logistic regression analysis. There was a substantial agreement between the two raters for the detection of the T2-FLAIR mismatch sign (Cohen's kappa coefficient was 0.647). The T2-FLAIR mismatch sign when co-registered with the degree of tumor homogeneity were significant predictors of the IDH status (OR 29.642; 95% CI 1.73-509.15, p = 0.019). The probability of being IDH mutant in the presence of T2-FLAIR mismatch sign was as high as 92.9% (95% CI 63-99%). The sensitivity and specificity of T2-FLAIR mismatch sign in the detection of the IDH mutation was 88.9% and 86.7%, respectively. The T2-FLAIR mismatch sign may be an easy to use and helpful tool in recognizing IDH mutant patients, particularly if formal IDH testing is not available. We suggest that the adoption of a protocol based on imaging and histological data for optimal glioma characterization could be very helpful.

The influence of subventricular zone involvement in extent of resection and tumor growth pattern of glioblastoma

Objectives

Isocitrate dehydrogenase (IDH1/2) mutations and O6-alkylguanine DNA methyltransferase (MGMT) promoter methylations are acknowledged survival predictors in patients with glioblastoma (GB). Moreover, tumor growth patterns like multifocality and subventricular zone (SVZ) involvement seem to be associated with poorer outcomes. Here, we wanted to evaluate the influence of the SVZ involvement and the multifocal tumor growth on the extent of surgical resection and its correlation with overall survival (OS) and molecular characteristics of patients with GB.

Methods

Adult patients with primary GB who underwent surgery at our department between 2012 and 2014 were included. Preoperative magnetic resonance imaging findings were analyzed with regard to tumor location, presence of multifocality and SVZ involvement. The extent of surgical resection as well as clinical and molecular parameters was collected from electronic patient records. Univariate and multivariate analyses were performed.

Results

Two hundred eight patients were retrospectively analyzed, comprising 90 (43.3%) female individuals with a mean age of 62.9 (±12.26) years and OS of 10.2 months (±8.9). Unifocal tumor location was a predictor for better OS with a mean of 11.4 (±9.4) months (vs. 8.0 [±7.4] months, p=0.008). Affection of the SVZ was also associated with lower surgical resection rates (p<0.001). SVZ involvement revealed with 7.8 (±7.0) months a significant worse OS [vs. 13.9 (±10.1) months, p<0.001]. All six IDH1/2 wildtype tumors showed an unifocal location (p=0.066). MGMT promoter methylation was not associated with multifocal tumor growth (p=0.649) or SVZ involvement (p=0.348). Multivariate analysis confirmed independent association between the SVZ involvement and OS (p=0.001).

Conclusion

The involvement of the SVZ appears to have an influence on a lower resection rate of GB. This negative impact of SVZ on GB outcome might be related to lesser extent of resection, higher rates of multifocality and greater surgical morbidity but not inevitably to IDH1/2 mutation and MGMT promoter methylation status.

Glioblastomas located in proximity to the subventricular zone (SVZ) exhibited enrichment of gene expression profiles associated with the cancer stem cell state

INTRODUCTION

Conflicting results have been reported in the association between glioblastoma proximity to the subventricular zone (SVZ) and enrichment of cancer stem cell properties. Here, we examined this hypothesis using magnetic resonance (MR) images derived from 217 The Cancer Imaging Archive (TCIA) glioblastoma subjects.

METHODS

Pre-operative MR images were segmented automatically into contrast enhancing (CE) tumor volumes using Iterative Probabilistic Voxel Labeling (IPVL). Distances were calculated from the centroid of CE tumor volumes to the SVZ and correlated with gene expression profiles of the corresponding glioblastomas. Correlative analyses were performed between SVZ distance, gene expression patterns, and clinical survival.

RESULTS

Glioblastoma located in proximity to the SVZ showed increased mRNA expression patterns associated with the cancer stem-cell state, including CD133 (P = 0.006). Consistent with the previous observations suggesting that glioblastoma stem cells exhibit increased DNA repair capacity, glioblastomas in proximity to the SVZ also showed increased expression of DNA repair genes, including MGMT (P = 0.018). Reflecting this enhanced DNA repair capacity, the genomes of glioblastomas in SVZ proximity harbored fewer single nucleotide polymorphisms relative to those located distant to the SVZ (P = 0.003). Concordant with the notion that glioblastoma stem cells are more aggressive and refractory to therapy, patients with glioblastoma in proximity to SVZ exhibited poorer progression free and overall survival (P < 0.01).

CONCLUSION

An unbiased analysis of TCIA suggests that glioblastomas located in proximity to the SVZ exhibited mRNA expression profiles associated with stem cell properties, increased DNA repair capacity, and is associated with poor clinical survival.

Hypoxia Inducible Factors' Signaling in Pediatric High-Grade Gliomas: Role, Modelization and Innovative Targeted Approaches

The brain tumor microenvironment has recently become a major challenge in all pediatric cancers, but especially in brain tumors like high-grade gliomas. Hypoxia is one of the extrinsic tumor features that interacts with tumor cells, but also with the blood-brain barrier and all normal brain cells. It is the result of a dramatic proliferation and expansion of tumor cells that deprive the tissues of oxygen inflow. However, cancer cells, especially tumor stem cells, can endure extreme hypoxic conditions by rescheduling various genes' expression involved in cell proliferation, metabolism and angiogenesis and thus, promote tumor expansion, therapeutic resistance and metabolic adaptation. This cellular adaptation implies Hypoxia-Inducible Factors (HIF), namely HIF-1α and HIF-2α. In pediatric high-grade gliomas (pHGGs), several questions remained open on hypoxia-specific role in normal brain during gliomagenesis and pHGG progression, as well how to model it in preclinical studies and how it might be counteracted with targeted therapies. Therefore, this review aims to gather various data about this key extrinsic tumor factor in pHGGs.

Clinical Significance of Fractional Anisotropy Measured in Peritumoral Edema as a Biomarker of Overall Survival in Glioblastoma: Evidence Using Correspondence Analysis

Introduction

Fractional anisotropy (FA), a diffusion tensor image (DTI) derived biomarker is related to invasion, infiltration, and extension of glioblastoma (GB). We aimed to evaluate FA values and their association with intervals of overall survival (OS).

Materials and Methods

Retrospective study conducted in 36 patients with GB included 23 (63.9%) males, 46 ± 14 y; and 13 (36.1%) females, 53 ± 13; followed up for 36 months. We measured FA at edema, enhancing rim, and necrosis. We created two categorical variables using levels of FA and intervals of OS to evaluate their relationships. Kaplan-Meier method and correspondence analysis evaluated the association between OS (grouped in 7 six-month intervals) and FA measurements.

Results

Median FA values were higher in healthy brain regions (0.351), followed by peritumoral edema (0.190), enhancing ring (0.116), and necrosis (0.071). Pair-wise comparisons among tumor regions showed a significant difference, P < 0.001. The median OS for all patients was 19.3 months; variations in the OS curves among subgroups was significant χ² (3) = 8.48, P = 0.037. Correspondence analysis showed a significant association between FA values in the edema region and the survival intervals χ² (18) = 30.996, P = 0.029.

Conclusions

Alternative multivariate assessment using correspondence analysis might supplement the traditional survival analysis in patients with GB. A close follow-up of the variability of FA in the peritumoral edema region is predictive of the OS within specific six-month interval subgroup. Further studies should focus on predictive models combining surgical and DTI biomarkers.

Ventricle contact is associated with lower survival and increased peritumoral perfusion in glioblastoma

OBJECTIVE

The purpose of this study was to prospectively investigate outcome and differences in peritumoral MRI characteristics of glioblastomas (GBMs) that were in contact with the ventricles (ventricle-contacting tumors) and those that were not (noncontacting tumors). GBMs are heterogeneous tumors with variable survival. Lower survival is suggested for patients with ventricle-contacting tumors than for those with noncontacting tumors. This might be supported by aggressive peritumoral MRI features. However, differences in MRI characteristics of the peritumoral environment between ventricle-contacting and noncontacting GBMs have not yet been investigated.

METHODS

Patients with newly diagnosed GBM underwent preoperative MRI with contrast-enhanced T1-weighted, FLAIR, diffusion-weighted, and perfusion-weighted sequences. Tumors were categorized into ventricle-contacting or noncontacting based on contrast enhancement. Survival analysis was performed using log-rank for univariate analysis and Cox regression for multivariate analysis. Normalized perfusion (relative cerebral blood volume [rCBV]) and diffusion (apparent diffusion coefficient [ADC]) values were calculated in 2 regions: the peritumoral nonenhancing FLAIR region overlapping the subventricular zone and the remaining peritumoral nonenhancing FLAIR region.

RESULTS

Overall survival was significantly lower for patients with contacting tumors than for those with noncontacting tumors (434 vs 747 days, p < 0.001). Progression-free survival showed a comparable trend (260 vs 375 days, p = 0.094). Multivariate analysis confirmed a survival difference for both overall survival (HR 3.930, 95% CI 1.740-8.875, p = 0.001) and progression-free survival (HR 2.506, 95% CI 1.254-5.007, p = 0.009). Peritumoral perfusion was higher in contacting than in noncontacting tumors for both FLAIR regions (p = 0.04). There was no difference in peritumoral ADC values between the 2 groups.

CONCLUSIONS

Patients with ventricle-contacting tumors had poorer outcomes than patients with noncontacting tumors. This disadvantage of ventricle contact might be explained by higher peritumoral perfusion leading to more aggressive behavior.

Location-Dependent Patient Outcome and Recurrence Patterns in IDH1-Wildtype Glioblastoma

Recent studies suggest that glioblastomas (GBMs) contacting the subventricular zone (SVZ) as the main adult neurogenic niche confer a dismal prognosis but disregard the unique molecular and prognostic phenotype associated with isocitrate dehydrogenase 1 (IDH1) mutations. We therefore examined location-dependent prognostic factors, growth, and recurrence patterns in a consecutive cohort of 285 IDH1-wildtype GBMs. Based on pre-operative contrast-enhanced MRI, patients were allotted to four location-dependent groups with (SVZ+; groups I, II) and without (SVZ-; groups III, IV) SVZ involvement or with (cortex+; groups I, III) and without (cortex-; groups II, IV) cortical involvement and compared for demographic, treatment, imaging, and survival data at first diagnosis and recurrence. SVZ involvement was associated with lower Karnofsky performance score (p < 0.001), lower frequency of complete resections at first diagnosis (p < 0.0001), and lower non-surgical treatment intensity at recurrence (p < 0.001). Multivariate survival analysis employing a Cox proportional hazards model identified SVZ involvement as an independent prognosticator of inferior overall survival (p < 0.001) and survival after relapse (p = 0.041). In contrast, multifocal growth at first diagnosis (p = 0.031) and recurrence (p < 0.001), as well as distant recurrences (p < 0.0001), was more frequent in cortex+ GBMs. These findings offer the prospect for location-tailored prognostication and treatment based on factors assessable on pre-operative MRI.

The role of inflammation in subventricular zone cancer

The adult subventricular zone (SVZ) stem cell niche has proven vital for discovering neurodevelopmental mechanisms and holds great potential in medicine for neurodegenerative diseases. Yet the SVZ holds a dark side - it can become tumorigenic. Glioblastomas can arise from the SVZ via cancer stem cells (CSCs). Glioblastoma and other brain cancers often have dismal prognoses since they are resistant to treatment. In this review we argue that the SVZ is susceptible to cancer because it contains stem cells, migratory progenitors and unusual inflammation. Theoretically, SVZ stem cells can convert to CSCs more readily than can postmitotic neural cells. Additionally, the robust long-distance migration of SVZ progenitors can be subverted upon tumorigenesis to an infiltrative phenotype. There is evidence that the SVZ, even in health, exhibits chronic low-grade cellular and molecular inflammation. Its inflammatory response to brain injuries and disease differs from that of other brain regions. We hypothesize that the SVZ inflammatory environment can predispose cells to novel mutations and exacerbate cancer phenotypes. This can be studied in animal models in which human mutations related to cancer are knocked into the SVZ to induce tumorigenesis and the CSC immune interactions that precede full-blown cancer. Importantly inflammation can be pharmacologically modulated providing an avenue to brain cancer management and treatment. The SVZ is accessible by virtue of its location surrounding the lateral ventricles and CSCs in the SVZ can be targeted with a variety of pharmacotherapies. Thus, the SVZ can yield aggressive tumors but can be targeted via several strategies.

The Pathophysiology of Post-Traumatic Glioma

Malignant glioma is a brain tumor with a very high mortality rate resulting from the specific morphology of its infiltrative growth and poor early detection rates. The causes of one of its very specific types, i.e., post-traumatic glioma, have been discussed for many years, with some studies providing evidence for mechanisms where the reaction to an injury may in some cases lead to the onset of carcinogenesis in the brain. In this review of the available literature, we discuss the consequences of breaking the blood–brain barrier and consequences of the influx of immune-system cells to the site of injury. We also analyze the influence of inflammatory mediators on the expression of genes controlling the process of apoptosis and the effect of chemical mutagenic factors on glial cells in the brain. We present the results of experimental studies indicating a relationship between injury and glioma development. However, epidemiological studies on post-traumatic glioma, of which only a few confirm the conclusions of experimental research, indicate that any potential relationship between injury and glioma, if any, is indirect.

Role of amino-acid PET in high-grade gliomas: limitations and perspectives

Positron emission tomography (PET) using radiolabeled amino-acids was recently recommended by the Response Assessment in Neuro-Oncology (RANO) working group as an additional tool in the diagnostic assessment of brain tumors. The aim of this review is to summarize available literature data on the role of amino-acid PET imaging in high-grade gliomas (HGGs), with regard to diagnosis, treatment planning and follow-up of these tumors. Indeed, amino-acid PET applications are multiple throughout the evolution of HGGs. However, certain limitations such as lack of specificity, uncertain value for grading and prognostication or the limited data for treatment monitoring should to be taken into account, the latter of which are further developed in this review. Notwithstanding these limitations, amino-acid PET is becoming increasingly accessible in many nuclear medicine centers. Larger prospective cohort prospective studies are thus needed in order to increase the clinical value of this modality and enable its extended use to the largest number of patients.

Evolutionary basis of a new gene- and immune-therapeutic approach for the treatment of malignant brain tumors: from mice to clinical trials for glioma patients

Glioma cells are one of the most aggressive and malignant tumors. Following initial surgery, and radio-chemotherapy they progress rapidly, so that patients' median survival remains under two years. They invade throughout the brain, which makes them difficult to treat, and are universally lethal. Though total resection is always attempted it is not curative. Standard of care in 2016 comprises surgical resection, radiotherapy and chemotherapy (temozolomide). Median survival is currently ~14-20months post-diagnosis though it can be higher in high complexity medical university centers, or during clinical trials. Why the immune system fails to recognize the growing brain tumor is not completely understood. We believe that one reason for this failure is that the brain lacks cells that perform the role that dendritic cells serve in other organs. The lack of functional dendritic cells from the brain causes the brain to be deficient in priming systemic immune responses to glioma antigens. To overcome this drawback we reconstituted the brain immune system for it to initiate and prime anti-glioma immune responses from within the brain. To achieve brain immune reconstitution adenoviral vectors are injected into the resection cavity or remaining tumor. One adenoviral vector expresses the HSV-1 derived thymidine kinase which converts ganciclovir into phospho-ganciclovir which becomes cytotoxic to dividing cells. The second adenovirus expresses the cytokine fms-like tyrosine kinase 3 ligand (Flt3L). Flt3L differentiates precursors into dendritic cells and acts as a chemokine for dendritic cells. This results in HSV-1/ganciclovir killing of tumor cells, and the release of tumor antigens, which are then taken up by dendritic cells recruited to the brain tumor microenvironment by Flt3L. Concomitant release of HMGB1, a TLR2 agonist that activates dendritic cells, stimulates dendritic cells loaded with glioma antigens to migrate to the cervical lymph nodes to prime a systemic CD8+ T cytotoxic killing of brain tumor cells. This induced immune response causes glioma-specific cytotoxicity, induces immunological memory, and does not cause brain toxicity or autoimmunity. A Phase I Clinical Trial, to test our hypothesis in human patients, was opened in December 2013 (see: NCT01811992, Combined Cytotoxic and Immune-Stimulatory Therapy for Glioma, at ClinicalTrials.gov). This trial is a first in human trial to test whether the re-engineering of the brain immune system can serve to treat malignant brain tumors. The long and winding road from the laboratory to the clinical trial follows below.

Clinical correlates of subventricular zone-contacting glioblastomas: a meta-analysis

INTRODUCTION

The clinical and molecular correlates of glioblastomas (GBMs) contacting the subventricular zone (SVZ+ GBM) are unknown. This work aimed to reveal any such correlates that may help explain their increased GBM malignancy.

EVIDENCE ACQUISITION

A meta-analysis was, therefore, conducted to assess whether tumor's MGMT promoter methylation status, isocitrate dehydrogenase (IDH) mutation status, volume, and extent of resection as well as patients' age at diagnosis and preoperative Karnofsky performance status score (KPS) correlate with SVZ contact by GBM. In addition, available imaging of GBM patients in The Cancer Imaging Archive was assessed for SVZ contact and their corresponding clinical and molecular variables were obtained through The Cancer Genome Atlas (TCGA) database.

EVIDENCE SYNTHESIS

Twenty-one studies were identified through PubMed and EMBASE database search. This review included 257 patients identified from the TCIA/TCGA database. MGMT promoter methylation status (summary odds ratio [OD], 1.18 [0.84-1.66], P=0.34), IDH mutation status (OD: 0.63 [0.20-1.99], P=0.43), and patients' age of diagnosis (summary mean difference, MD, 0.10 years [-1.85, 2.05], P=0.92) did not associated with SVZ contact of the GBM. However, SVZ+ GBMs were significantly larger than SVZ- GBMs (MD: 17.3 cm3 [8.70-25.8], P<0.0001). SVZ+ GBM patients had lower KPS scores (MD: -3.33 [-5.31-(-1.35)], P=0.001) and were half as likely to receive a gross total resection (OD: 0.50 [0.40-0.64], P<0.00001).

CONCLUSIONS

Additional, large studies that rigorously control for all the known clinical and molecular prognosticators, especially extent of resection and preoperative KPS scores, are needed to evaluate whether SVZ contact by GBM independently influences survival.

Influence of glioblastoma contact with the lateral ventricle on survival: a meta-analysis

The ventricular-subventricular zone (V-SVZ), which lies in the walls of the lateral ventricles (LV), is the largest neurogenic niche within the adult brain. Whether radiographic contact with the LV influences survival in glioblastoma (GBM) patients remains unclear. We assimilated and analyzed published data comparing survival in GBM patients with (LV+GBM) and without (LV-GBM) radiographic LV contact. PubMed, EMBASE, and Cochrane electronic databases were searched. Fifteen studies with survival data on LV+GBM and LV-GBM patients were identified. Their Kaplan-Meier survival curves were digitized and pooled for generation of median overall (OS) and progression free (PFS) survivals and log-rank hazard ratios (HRs). The log-rank and reported multivariate HRs after accounting for the common predictors of GBM survival were analyzed separately by meta-analyses. The calculated median survivals (months) from pooled data were 12.95 and 16.58 (OS), and 4.54 and 6.25 (PFS) for LV+GBMs and LV-GBMs, respectively, with an overall log-rank HRs of 1.335 [1.204-1.513] (OS) and 1.387 [1.225-1.602] (PFS). Meta-analysis of log-rank HRs resulted in summary HRs of 1.58 [1.35-1.85] (OS, 10 studies) and 1.41 [1.22-1.64] (PFS, 5 studies). Meta-analysis of multivariate HRs resulted in summary HRs of 1.35 [1.14-1.58] (OS, 6 studies) and 1.64 [0.88-3.05] (PFS, 3 studies). Patients with GBM contacting the LV have lower survival. This effect may be independent of the common predictors of GBM survival, suggesting a clinical influence of V-SVZ contact on GBM biology.

Traumatic brain injury and subsequent glioblastoma development: Review of the literature and case reports

BACKGROUND

Previous reports have proposed an association between traumatic brain injury (TBI) and subsequent glioblastoma (GBM) formation.

METHODS

We used literature searches and radiographic evidence from two patients to assess the possibility of a link between TBI and GBM.

RESULTS

Epidemiological studies are equivocal on a possible link between brain trauma and increased risk of malignant glioma formation. We present two case reports of patients with GBM arising at the site of prior brain injury.

CONCLUSION

The hypothesis that TBI may predispose to gliomagenesis is disputed by several large-scale epidemiological studies, but supported by some. Radiographic evidence from two cases presented here suggest that GBM formed at the site of brain injury. We propose a putative pathogenesis model that connects post-traumatic inflammation, stem and progenitor cell transformation, and gliomagenesis.

Do Increased Doses to Stem-Cell Niches during Radiation Therapy Improve Glioblastoma Survival?

Background and Purpose. The reasons for the inevitable glioblastoma recurrence are yet understood. However, recent data suggest that tumor cancer stem cells (CSCs) in the stem-cell niches, with self-renewing capacities, might be responsible for tumor initiation, propagation, and recurrence. We aimed to analyze the effect of higher radiation doses to the stem-cell niches on progression-free survival (PFS) and overall survival (OS) in glioblastoma patients. Materials and Methods. Sixty-five patients with primary glioblastoma treated with radiation therapy were included in this retrospective analysis. The SVZ and DG were segmented on treatment planning magnetic resonance imaging, and the dose distributions to the structures were calculated. The relationship of dosimetry data and survival was evaluated using the Cox regression analysis. Results. Conventionally fractionated patients (n = 54) who received higher doses (D_mean ≥ 40 Gy) to the IL SVZ showed improved PFS (8.5 versus 5.2 months; p = 0.013). Furthermore, higher doses (D_mean ≥ 30 Gy) to the CL SVZ were associated with increased PFS (10.1 versus 6.9 months; p = 0.025). Conclusion. Moderate higher IL SVZ doses (≥40 Gy) and CL SVZ doses (≥30 Gy) are associated with improved PFS. Higher doses to the DG, the second stem-cell niche, did not influence the survival. Targeting the potential cancer stem cells in the SVZ might be a promising treatment approach for glioblastoma and should be addressed in a prospective randomized trial.

Anatomical Involvement of the Subventricular Zone Predicts Poor Survival Outcome in Low-Grade Astrocytomas

The subventricular zone (SVZ) has been implicated in the origination, development, and biological behavior of gliomas. Tumor-SVZ contact is also postulated to be a poor prognostic factor in glioblastomas. We aimed to evaluate the prognostic consequence of the anatomical involvement of low-grade gliomas with the SVZ. To that end, we reviewed 143 patients with diffuse astrocytomas, and tumor lesions were manually delineated on magnetic resonance images. We initially investigated the prognostic role of SVZ contact in all patients. Additionally, we investigated the influence of the anatomical proximity of the tumor lesion centroids to the SVZ in the SVZ-involved patient cohorts, as well as location within the SVZ. We found SVZ contact with tumors to be a significant prognostic factor of overall survival in all patients with diffuse astrocytomas (p = 0.027). In the SVZ-involved cohort, a shorter distance from the tumor centroid to the SVZ (≤30 mm) correlated with shorter overall survival (p = 0.022) on univariate analysis. However, there was no significant difference in overall survival with respect to the SVZ region involved with the tumor (p = 0.930). Multivariate analysis showed that a shorter distance between the tumor centroid and the SVZ (p = 0.039) was significantly associated with poor overall survival in SVZ-involved patients. Hence, this study helps establish the prognostic role of the anatomical interaction of tumors with the SVZ in low-grade astrocytomas.

The Long and Winding Road: From the High-Affinity Choline Uptake Site to Clinical Trials for Malignant Brain Tumors

Malignant brain tumors are one of the most lethal cancers. They originate from glial cells which infiltrate throughout the brain. Current standard of care involves surgical resection, radiotherapy, and chemotherapy; median survival is currently ~14-20 months postdiagnosis. Given that the brain immune system is deficient in priming systemic immune responses to glioma antigens, we proposed to reconstitute the brain immune system to achieve immunological priming from within the brain. Two adenoviral vectors are injected into the resection cavity or remaining tumor. One adenoviral vector expresses the HSV-1-derived thymidine kinase which converts ganciclovir into a compound only cytotoxic to dividing glioma cells. The second adenovirus expresses the cytokine fms-like tyrosine kinase 3 ligand (Flt3L). Flt3L differentiates precursors into dendritic cells and acts as a chemokine that attracts dendritic cells to the brain. HSV-1/ganciclovir killing of tumor cells releases tumor antigens that are taken up by dendritic cells within the brain tumor microenvironment. Tumor killing also releases HMGB1, an endogenous TLR2 agonist that activates dendritic cells. HMGB1-activated dendritic cells, loaded with glioma antigens, migrate to cervical lymph nodes to stimulate a systemic CD8+ T cells cytotoxic immune response against glioma. This immune response is specific to glioma tumors, induces immunological memory, and does neither cause brain toxicity nor autoimmune responses. An IND was granted by the FDA on 4/7/2011. A Phase I, first in person trial, to test whether reengineering the brain immune system is potentially therapeutic is ongoing.

Reconstructed Metabolic Network Models Predict Flux-Level Metabolic Reprogramming in Glioblastoma

Developments in genome scale metabolic modeling techniques and omics technologies have enabled the reconstruction of context-specific metabolic models. In this study, glioblastoma multiforme (GBM), one of the most common and aggressive malignant brain tumors, is investigated by mapping GBM gene expression data on the growth-implemented brain specific genome-scale metabolic network, and GBM-specific models are generated. The models are used to calculate metabolic flux distributions in the tumor cells. Metabolic phenotypes predicted by the GBM-specific metabolic models reconstructed in this work reflect the general metabolic reprogramming of GBM, reported both in in-vitro and in-vivo experiments. The computed flux profiles quantitatively predict that major sources of the acetyl-CoA and oxaloacetic acid pool used in TCA cycle are pyruvate dehydrogenase from glycolysis and anaplerotic flux from glutaminolysis, respectively. Also, our results, in accordance with recent studies, predict a contribution of oxidative phosphorylation to ATP pool via a slightly active TCA cycle in addition to the major contributor aerobic glycolysis. We verified our results by using different computational methods that incorporate transcriptome data with genome-scale models and by using different transcriptome datasets. Correct predictions of flux distributions in glycolysis, glutaminolysis, TCA cycle and lipid precursor metabolism validate the reconstructed models for further use in future to simulate more specific metabolic patterns for GBM.

Population-based MRI atlases of spatial distribution are specific to patient and tumor characteristics in glioblastoma

BACKGROUND AND PURPOSE

In treating glioblastoma (GB), surgical and chemotherapeutic treatment guidelines are, for the most part, independent of tumor location. In this work, we compiled imaging data from a large cohort of GB patients to create statistical atlases illustrating the disease spatial frequency as a function of patient demographics as well as tumor characteristics.

MATERIALS AND METHODS

Two-hundred-six patients with pathology-proven glioblastoma were included. Of those, 65 had pathology-proven recurrence and 113 had molecular subtype and genetic information. We used validated software to segment the tumors in all patients and map them from patient space into a common template. We then created statistical maps that described the spatial location of tumors with respect to demographics and tumor characteristics. We applied a chi-square test to determine whether pattern differences were statistically significant.

RESULTS

The most frequent location for glioblastoma in our patient population is the right temporal lobe. There are statistically significant differences when comparing patterns using demographic data such as gender (p = 0.0006) and age (p = 0.006). Small and large tumors tend to occur in separate locations (p = 0.0007). The tumors tend to occur in different locations according to their molecular subtypes (p < 10(- 6)). The classical subtype tends to spare the frontal lobes, the neural subtype tend to involve the inferior right frontal lobe. Although the sample size is limited, there was a difference in location according to EGFR VIII genotype (p < 10(- 4)), with a right temporal dominance for EFGR VIII negative tumors, and frontal lobe dominance in EGFR VIII positive tumors.

CONCLUSIONS

Spatial location of GB is an important factor that correlates with demographic factors and tumor characteristics, which should therefore be considered when evaluating a patient with GB and might assist in personalized treatment.

A patient-specific computational model of hypoxia-modulated radiation resistance in glioblastoma using 18F-FMISO-PET

Glioblastoma multiforme (GBM) is a highly invasive primary brain tumour that has poor prognosis despite aggressive treatment. A hallmark of these tumours is diffuse invasion into the surrounding brain, necessitating a multi-modal treatment approach, including surgery, radiation and chemotherapy. We have previously demonstrated the ability of our model to predict radiographic response immediately following radiation therapy in individual GBM patients using a simplified geometry of the brain and theoretical radiation dose. Using only two pre-treatment magnetic resonance imaging scans, we calculate net rates of proliferation and invasion as well as radiation sensitivity for a patient's disease. Here, we present the application of our clinically targeted modelling approach to a single glioblastoma patient as a demonstration of our method. We apply our model in the full three-dimensional architecture of the brain to quantify the effects of regional resistance to radiation owing to hypoxia in vivo determined by [(18)F]-fluoromisonidazole positron emission tomography (FMISO-PET) and the patient-specific three-dimensional radiation treatment plan. Incorporation of hypoxia into our model with FMISO-PET increases the model-data agreement by an order of magnitude. This improvement was robust to our definition of hypoxia or the degree of radiation resistance quantified with the FMISO-PET image and our computational model, respectively. This work demonstrates a useful application of patient-specific modelling in personalized medicine and how mathematical modelling has the potential to unify multi-modality imaging and radiation treatment planning.

Stem cell niche irradiation in glioblastoma: providing a ray of hope?

Glioblastomas are organized hierarchically with a small number of glioblastoma stem cells that have unique self-renewal capacity and multilineage potency. The subventricular zone (SVZ) constitutes the largest neural stem cell niche in the adult human brain; it may also act as a reservoir of glioblastoma stem cells that can initiate, promote or repopulate a tumor. Incidental irradiation of SVZ has been shown to potentially influence outcomes suggesting that aggressively targeting the stem cell niche may offer a ray of hope in glioblastoma. The following review provides a summary of the experimental evidence supporting the origin and location of the putative glioblastoma stem cell in the SVZ, and offers a critical appraisal of the growing body of clinical evidence correlating SVZ dosimetry with outcomes in glioblastoma.

Use of preoperative FLAIR MRI and ependymal proximity of tumor enhancement as surrogate markers of brain tumor origin

Neural stem cells proliferate in the subventricular zone and give rise to progeny that differentiate and migrate throughout the brain. We aimed to test the hypothesis that glioma behavior and grade may correlate with the identity of the tumor cell of origin. We evaluated three preoperative radiographic features (fluid attenuated inversion recovery [FLAIR] MRI characteristics, tumor proximity to ventricular ependyma, and subependymal representation) as surrogate markers of tumor origin using a retrospective cohort design. The medical records of 228 patients who underwent surgical resection of a glioma from January 2004 to August 2008 were reviewed. Average patient age was 54.5 years (standard deviation [SD] 15.3) with a male predominance (62.9%). World Health Organization glioma grades amongst the cohort were Grade IV (71.6%), Grade III (21.3%) and Grade II (7.1%). Mean survival was 11.2 months (SD 10.5) with a mean follow up of 12.8 months (SD 11.3). Glioma tumor grade was significantly correlated to FLAIR signal proximity to the ependymal surface (p<0.01) and inversely with proximity of tumor mass to the ependyma (p<0.01). The mean distance of tumor-associated FLAIR signal from the ependymal surface for glioblastoma multiforme (GBM) was 1.2mm (SD 3.3) compared to 4.8 (SD 6.5) for anaplastic astrocytomas and 6.6mm (SD 6.7; p<0.01) for low grade gliomas. Conversely, the mean distance of the enhancing tumor mass from the ependyma for GBM was 7.3mm (SD 9.4), Grade III glioma 2.3mm (SD 4.9), and Grade II glioma 3.8mm (SD 6.8; p<0.05). These findings suggest that higher grade gliomas might arise from less differentiated neuroepithelial cells in the subventricular zone that possess greater migratory potential.

Can lateral ventricle contact predict the ontogeny and prognosis of glioblastoma?

Lateral ventricle contact (LVC) by glioblastomas has been proposed to reveal their origin and may have prognostic value; however, results from previous studies have been controversial. This study explored the association between LVC and tumor origin and prognosis in glioblastoma patients. Magnetic resonance imaging and clinical data from 115 glioma patients were retrospectively reviewed, and Kaplan-Meier analysis and Cox proportional hazards models were used to assess the occurrence of LVC as a function of survival in 43 glioblastoma patients. The mRNA expression profiles were compared by microarray analysis in LV-contacting and non-LV-contacting glioblastomas (LVCGs and NLVCGs, respectively). The sphere-forming and invasive capabilities of LVCG- and NLVCG-derived stem cells were compared in primary glioma stem cell cultures with tumorsphere formation and Matrigel assays, respectively. LVC was more frequently detected in high-grade gliomas which, along with LVCGs, were significantly larger than low-grade gliomas and NLVCGs. LVC parameters were not independent predictors of glioblastoma patient prognosis; the expression profiles (including stemness genes expression) were similar between LVCGs and NLVCGs, and no significant differences were observed in tumorsphere-forming capacity and invasiveness between stem cells derived from the two glioblastoma types. Our results suggest that the origin of glioblastomas cannot be simply estimated by radiographic LVC, and after standard therapy the prognostic value of LVC needs to be carefully interpreted.

Anatomic features of glioblastoma and their potential impact on survival

BACKGROUND

Many reports on glioblastoma multiforme discuss the prognostic impact of anatomical features such as cysts, necrotic changes, extent of edema or subependymal spread of tumor cells. In the present study, we examined different growth patterns and their possible relations to patient survival.

METHODS

To analyze whether anatomical characteristics are related to prognosis, we reviewed the prospectively collected pre- and postoperative MRIs of 83 patients in the 5-ALA study, provided by the 5-ALA Glioma Study Group. Following a standardized analytic work flow, the tumor volume and site, presence of necrosis or cysts, and perifocal edema were assessed preoperatively. In the same way, postoperative MRI and the MRI at first recurrence were analyzed. In addition, survival time of the patients was documented.

RESULTS

Median survival time of all 83 patients was 15.1 months (range 1.5 to 70.1, mean 18). The site or volume of glioblastoma, as well as the presence of intratumoral necrosis or cysts, did not exert a significant effect on survival time; 96.4 % of recurrences occurred within the former resection margin. Tumors with initial contact with the subependymal zone had multifocal or ventricular recurrences significantly more often. In patients with residual tumor on early postoperative MRI, the follow-up images displayed enlargement of the remnants in 91.9 % of these cases.

CONCLUSIONS

A merely anatomical analysis of the glioblastoma growth pattern cannot reliably provide prognostic information. The occurrence of most recurrences next to the resection margin and the high percentage of growing residual tumors underline the importance of complete resections.

Expert-validated CSF segmentation of MNI atlas enhances accuracy of virtual glioma growth patterns

Biomathematical modeling of glioma growth has been developed to optimize treatments delivery and to evaluate their efficacy. Simulations currently make use of anatomical knowledge from standard MRI atlases. For example, cerebrospinal fluid (CSF) spaces are obtained by automatic thresholding of the MNI atlas, leading to an approximate representation of real anatomy. To correct such inaccuracies, an expert-revised CSF segmentation map of the MNI atlas was built. Several virtual glioma growth patterns of different locations were generated, with and without using the expert-revised version of the MNI atlas. The adequacy between virtual and radiologically observed growth patterns was clearly higher when simulations were based on the expert-revised atlas. This work emphasizes the need for close collaboration between clinicians and researchers in the field of brain tumor modeling.

Loss of p53 cooperates with K-ras activation to induce glioma formation in a region-independent manner

Gliomas are recognized as a heterogeneous group of neoplasms differing in their location and morphological features. These differences, between and within varying grades of gliomas, have not been explained solely on the grounds of an oncogenic stimulus. Interactions with the tumor microenvironment as well as inherent characteristics of the cell of origin are likely a source of this heterogeneity. There is an ongoing debate over the cell of origin of gliomas, where some suggest a progenitor, while others argue for a stem cell origin. Thus, it is presumed that neurogenic regions of the brain such as the subventricular zone (SVZ) containing large numbers of neural stem and progenitor populations are more susceptible to transformation. Our studies demonstrate that K-ras(G12D) cooperates with the loss of p53 to induce gliomas from both the SVZ and cortical region, suggesting that cells in the SVZ are not uniquely gliomagenic. Using combinations of doxycycline-inducible K-ras(G12D) and p53 loss, we show that tumors induced by the cooperative actions of these genes remain dependent on active K-ras expression, as deinduction of K-ras(G12D) leads to complete tumor regression despite absence of p53. These results suggest that the interplay between specific combinations of genetic alterations and susceptible cell types, rather than the site of origin, are important determinates of gliomagenesis. Additionally, this model supports the view that, although several genetic events may be necessary to confer traits associated with oncogenic transformation, inactivation of a single oncogenic partner can undermine tumor maintenance, leading to regression and disease remission.

Glioblastoma-initiating cells: relationship with neural stem cells and the micro-environment

Glioblastoma multiforme (GBM, WHO grade IV) is the most common and lethal subtype of primary brain tumor with a median overall survival of 15 months from the time of diagnosis. The presence in GBM of a cancer population displaying neural stem cell (NSC) properties as well as tumor-initiating abilities and resistance to current therapies suggests that these glioblastoma-initiating cells (GICs) play a central role in tumor development and are closely related to NSCs. However, it is nowadays still unclear whether GICs derive from NSCs, neural progenitor cells or differentiated cells such as astrocytes or oligodendrocytes. On the other hand, NSCs are located in specific regions of the adult brain called neurogenic niches that have been shown to control critical stem cell properties, to nourish NSCs and to support their self-renewal. This “seed-and-soil” relationship has also been adapted to cancer stem cell research as GICs also require a specific micro-environment to maintain their “stem cell” properties. In this review, we will discuss the controversies surrounding the origin and the identification of GBM stem cells and highlight the micro-environment impact on their biology.

A practical scoring system to determine whether to proceed with surgical resection in recurrent glioblastoma

BACKGROUND

To determine the benefit of surgical management in recurrent glioblastoma, we analyzed a series of patients with recurrent glioblastoma who had undergone surgery, and we devised a new scale to predict their survival.

METHODS

Clinical data from 55 consecutive patients with recurrent glioblastoma were evaluated after surgical management. Kaplan-Meier survival analysis and Cox proportional hazards regression modeling were used to identify prognostic variables for the development of a predictive scale. After the multivariate analysis, performance status (P = .078) and ependymal involvement (P = .025) were selected for inclusion in the new prognostic scale. The devised scale was validated with a separate set of 96 patients from 3 different institutes.

RESULTS

A 3-tier scale (scoring range, 0-2 points) composed of additive scores for the Karnofsky performance status (KPS) (0 for KPS ≥ 70 and 1 for KPS < 70) and ependymal involvement (0 for no enhancement and 1 for enhancement of the ventricle wall in the magnetic resonance imaging) significantly distinguished groups with good (0 points; median survival, 18.0 months), intermediate (1 point; median survival, 10.0 months), and poor prognoses (2 points; median survival, 4.0 months). The new scale was successfully applied to the validation cohort of patients showing distinct prognosis among the groups (median survivals of 11.0, 9.0, and 4.0 months for the 0-, 1-, and 2-point groups, respectively).

CONCLUSIONS

We developed a practical scale to facilitate deciding whether to proceed with surgical management in patients with recurrent glioblastoma. This scale was useful for the diagnosis of prognostic groups and can be used to develop guidelines for patient treatment.

Modeling Tumor-Associated Edema in Gliomas during Anti-Angiogenic Therapy and Its Impact on Imageable Tumor

Glioblastoma, the most aggressive form of primary brain tumor, is predominantly assessed with gadolinium-enhanced T1-weighted (T1Gd) and T2-weighted magnetic resonance imaging (MRI). Pixel intensity enhancement on the T1Gd image is understood to correspond to the gadolinium contrast agent leaking from the tumor-induced neovasculature, while hyperintensity on the T2/FLAIR images corresponds with edema and infiltrated tumor cells. None of these modalities directly show tumor cells; rather, they capture abnormalities in the microenvironment caused by the presence of tumor cells. Thus, assessing disease response after treatments impacting the microenvironment remains challenging through the obscuring lens of MR imaging. Anti-angiogenic therapies have been used in the treatment of gliomas with spurious results ranging from no apparent response to significant imaging improvement with the potential for extremely diffuse patterns of tumor recurrence on imaging and autopsy. Anti-angiogenic treatment normalizes the vasculature, effectively decreasing vessel permeability and thus reducing tumor-induced edema, drastically altering T2-weighted MRI. We extend a previously developed mathematical model of glioma growth to explicitly incorporate edema formation allowing us to directly characterize and potentially predict the effects of anti-angiogenics on imageable tumor growth. A comparison of simulated glioma growth and imaging enhancement with and without bevacizumab supports the current understanding that anti-angiogenic treatment can serve as a surrogate for steroids and the clinically driven hypothesis that anti-angiogenic treatment may not have any significant effect on the growth dynamics of the overall tumor cell populations. However, the simulations do illustrate a potentially large impact on the level of edematous extracellular fluid, and thus on what would be imageable on T2/FLAIR MR. Additionally, by evaluating virtual tumors with varying growth kinetics, we see tumors with lower proliferation rates will have the most reduction in swelling from such treatments.

From patient-specific mathematical neuro-oncology to precision medicine

Gliomas are notoriously aggressive, malignant brain tumors that have variable response to treatment. These patients often have poor prognosis, informed primarily by histopathology. Mathematical neuro-oncology (MNO) is a young and burgeoning field that leverages mathematical models to predict and quantify response to therapies. These mathematical models can form the basis of modern “precision medicine” approaches to tailor therapy in a patient-specific manner. Patient-specific models (PSMs) can be used to overcome imaging limitations, improve prognostic predictions, stratify patients, and assess treatment response in silico. The information gleaned from such models can aid in the construction and efficacy of clinical trials and treatment protocols, accelerating the pace of clinical research in the war on cancer. This review focuses on the growing translation of PSM to clinical neuro-oncology. It will also provide a forward-looking view on a new era of patient-specific MNO.

Response classification based on a minimal model of glioblastoma growth is prognostic for clinical outcomes and distinguishes progression from pseudoprogression

Glioblastoma multiforme is the most aggressive type of primary brain tumor. Glioblastoma growth dynamics vary widely across patients, making it difficult to accurately gauge their response to treatment. We developed a model-based metric of therapy response called Days Gained that accounts for this heterogeneity. Here, we show in 63 newly diagnosed patients with glioblastoma that Days Gained scores from a simple glioblastoma growth model computed at the time of the first postradiotherapy MRI scan are prognostic for time to tumor recurrence and overall patient survival. After radiation treatment, Days Gained also distinguished patients with pseudoprogression from those with true progression. Because Days Gained scores can be easily computed with routinely available clinical imaging devices, this model offers immediate potential to be used in ongoing prospective studies.

Evaluation of heterogeneous metabolic profile in an orthotopic human glioblastoma xenograft model using compressed sensing hyperpolarized 3D 13C magnetic resonance spectroscopic imaging

High resolution compressed sensing hyperpolarized (13)C magnetic resonance spectroscopic imaging was applied in orthotopic human glioblastoma xenografts for quantitative assessment of spatial variations in (13)C metabolic profiles and comparison with histopathology. A new compressed sensing sampling design with a factor of 3.72 acceleration was implemented to enable a factor of 4 increase in spatial resolution. Compressed sensing 3D (13)C magnetic resonance spectroscopic imaging data were acquired from a phantom and 10 tumor-bearing rats following injection of hyperpolarized [1-(13)C]-pyruvate using a 3T scanner. The (13)C metabolic profiles were compared with hematoxylin and eosin staining and carbonic anhydrase 9 staining. The high-resolution compressed sensing (13)C magnetic resonance spectroscopic imaging data enabled the differentiation of distinct (13)C metabolite patterns within abnormal tissues with high specificity in similar scan times compared to the fully sampled method. The results from pathology confirmed the different characteristics of (13)C metabolic profiles between viable, non-necrotic, nonhypoxic tumor, and necrotic, hypoxic tissue.

Glioma revisited: from neurogenesis and cancer stem cells to the epigenetic regulation of the niche

Gliomas are the most incident brain tumor in adults. This malignancy has very low survival rates, even when combining radio- and chemotherapy. Among the gliomas, glioblastoma multiforme (GBM) is the most common and aggressive type, and patients frequently relapse or become refractory to conventional therapies. The fact that such an aggressive tumor can arise in such a carefully orchestrated organ, where cellular proliferation is barely needed to maintain its function, is a question that has intrigued scientists until very recently, when the discovery of the existence of proliferative cells in the brain overcame such challenges. Even so, the precise origin of gliomas still remains elusive. Thanks to new advents in molecular biology, researchers have been able to depict the first steps of glioma formation and to accumulate knowledge about how neural stem cells and its progenitors become gliomas. Indeed, GBM are composed of a very heterogeneous population of cells, which exhibit a plethora of tumorigenic properties, supporting the presence of cancer stem cells (CSCs) in these tumors. This paper provides a comprehensive analysis of how gliomas initiate and progress, taking into account the role of epigenetic modulation in the crosstalk of cancer cells with their environment.

Can irradiation of potential cancer stem-cell niche in the subventricular zone influence survival in patients with newly diagnosed glioblastoma?

Glioblastoma progenitor or stem cells residing in the stem-cell niche in the subventricular zones (SVZ) can initiate or promote tumorigenesis. They can also migrate throughout the brain, resulting in disease progression. Irradiation of potential cancer stem-cell niche in the SVZ may influence survival. To analyze radiotherapy dose-volume parameters to the SVZ that correlate with survival in adequately treated patients with newly diagnosed glioblastoma, 40 adults with histopathologically proven supratentorial glioblastoma with available baseline imaging treated with postoperative conventionally fractionated focal conformal radiotherapy plus chemotherapy, available radiotherapy planning dataset, and documented event of progression or death or minimum 6-month follow-up were included in this retrospective study. Dose-volume parameters to the SVZ were extracted from treatment planning system and analyzed in relation to survival outcomes. Mean ipsilateral and contralateral SVZ volumes were 5.6 and 6.4 cc, respectively. With median follow-up of 15 months (interquartile range 12-18 months), median [95 % confidence interval (CI)] progression-free survival (PFS) and overall survival (OAS) was 11 months (95 % CI 8.9-13.0 months) and 17 months (95 % CI 11.6-22.4 months), respectively. Older age (>50 years), poor recursive partitioning analysis (RPA) class, and higher than median of mean contralateral SVZ dose were associated with significantly worse PFS and OAS. Multivariate analysis identified RPA class, Karnofsky performance status, and mean ipsilateral SVZ dose as independent predictors of survival. Increasing mean dose to the ipsilateral SVZ was associated with significantly improved OAS. Irradiation of potential cancer stem-cell niche influences survival outcomes in patients with newly diagnosed glioblastoma.

The cellular origin for malignant glioma and prospects for clinical advancements

Glioma remains incurable despite great advancements in medicine. Targeting the cell of origin for gliomas could bring great hope for patients. However, as a collection of diverse diseases, each subtype of glioma could derive from a distinct cell of origin. To resolve such a complex problem, one must use multiple research approaches to gain deep insights. Here we review current evidence regarding the cell of origin from clinical observations, whole-genome molecular pathology and glioma animal models. We conclude that neural stem cells, glial progenitors (including oligodendrocyte progenitor cells) and astrocytes could all serve as cells of origin for gliomas, and that cells incurring initial mutations (cells of mutation) might not transform, while their progeny cells could instead transform and act as cells of origin. Further studies with multidisciplinary approaches are needed to link each subtype to a particular cell of origin, and to develop effective therapies that target the signaling network within these cells.

Mouse models to interrogate the implications of the differentiation status in the ontogeny of gliomas

Glioblastoma multiforme (GBM) is the most common and lethal of human primary central nervous system (CNS) tumors, with a median survival of 14-16 months despite optimal surgery, radiation and chemotherapy. A reason for this dismal prognosis is insufficient understanding of the ontogeny of GBMs, which are highly heterogeneous at a pathological level. This pathological diversity, between and within GBMs as well as varying grades of gliomas, has not been fully explained solely on the grounds of oncogenic stimulus. Interaction with the tumor microenvironment is likely a source of this pathological heterogeneity, as well as the inherent characteristics of the tumor cell of origin. Currently, controversy exists on whether the initial transformed cell is a differentiated astrocyte, progenitor or neural stem cell. Putative cancer stem cells (CSCs), which have features of normal stem cell plus the ability to recapitulate the tumor phenotype in vivo in small numbers, have been identified from a variety of solid human cancers, including GBMs. Evidence suggesting that regions harboring normal stem cells in the adult CNS, such as the subventricular zone and the dentate gyrus, are more prone to viral and chemical oncogenesis, is supportive of the hypothesis that brain tumors arise from stem cells. However, it is still to be determined whether the appearance of brain tumor stem cells (BTSC) is the cause or consequence of tumor initiation and progression. This review discusses emerging evidence highlighting the relevance of the state of differentiation and regional heterogeneity in the ontogeny of GBM. This is an area of high interest in cancer in general, with potential significant therapeutic and prognostic implications.

MADM gives new insights into gliomagenesis

In their recent paper, Liu et al. (2011) make use of an elegant genetic mouse model to study the formation of malignant brain tumors. Their findings add strong support to the growing body of evidence from several labs showing that some gliomas arise from oligodendrocyte precursor cells (OPCs). They also provide new insights, and raise new questions, regarding where, when, and how malignant gliomas form.

Glioblastoma models reveal the connection between adult glial progenitors and the proneural phenotype

BACKGROUND

Tumor heterogeneity is a major obstacle for finding effective treatment of Glioblastoma (GBM). Based on global expression analysis, GBM can be classified into distinct subtypes: Proneural, Neural, Classical and Mesenchymal. The signatures of these different tumor subtypes may reflect the phenotypes of cells giving rise to them. However, the experimental evidence connecting any specific subtype of GBM to particular cells of origin is lacking. In addition, it is unclear how different genetic alterations interact with cells of origin in determining tumor heterogeneity. This issue cannot be addressed by studying end-stage human tumors.

METHODOLOGY/PRINCIPAL FINDINGS

To address this issue, we used retroviruses to deliver transforming genetic lesions to glial progenitors in adult mouse brain. We compared the resulting tumors to human GBM. We found that different initiating genetic lesions gave rise to tumors with different growth rates. However all mouse tumors closely resembled the human Proneural GBM. Comparative analysis of these mouse tumors allowed us to identify a set of genes whose expression in humans with Proneural GBM correlates with survival.

CONCLUSIONS/SIGNIFICANCE

This study offers insights into the relationship between adult glial progenitors and Proneural GBM, and allows us to identify molecular alterations that lead to more aggressive tumor growth. In addition, we present a new preclinical model that can be used to test treatments directed at a specific type of GBM in future studies.