The role of telomere maintenance in the spontaneous growth arrest of pediatric low-grade gliomas

A new subtype of diffuse midline glioma, H3 K27 and BRAF/FGFR1 co-altered: a clinico-radiological and histomolecular characterisation

Diffuse midline gliomas (DMG) H3 K27-altered are incurable grade 4 gliomas and represent a major challenge in neuro-oncology. This tumour type is now classified in four subtypes by the 2021 edition of the WHO Classification of the Central Nervous System (CNS) tumours. However, the H3.3-K27M subgroup still appears clinically and molecularly heterogeneous. Recent publications reported that rare patients presenting a co-occurrence of H3.3K27M with BRAF or FGFR1 alterations tended to have a better prognosis. To better study the role of these co-driver alterations, we assembled a large paediatric and adult cohort of 29 tumours H3K27-altered with co-occurring activating mutation in BRAF or FGFR1 as well as 31 previous cases from the literature. We performed a comprehensive histological, radiological, genomic, transcriptomic and DNA methylation analysis. Interestingly, unsupervised t-distributed Stochastic Neighbour Embedding (tSNE) analysis of DNA methylation profiles regrouped BRAFV600E and all but one FGFR1MUT DMG in a unique methylation cluster, distinct from the other DMG subgroups and also from ganglioglioma (GG) or high-grade astrocytoma with piloid features (HGAP). This new DMG subtype harbours atypical radiological and histopathological profiles with calcification and/or a solid tumour component both for BRAFV600E and FGFR1MUT cases. The analyses of a H3.3-K27M BRAFV600E tumour at diagnosis and corresponding in vitro cellular model showed that mutation in H3-3A was the first event in the oncogenesis. Contrary to other DMG, these tumours occur more frequently in the thalamus (70% for BRAFV600E and 58% for FGFR1MUT) and patients have a longer overall survival with a median above three years. In conclusion, DMG, H3 K27 and BRAF/FGFR1 co-altered represent a new subtype of DMG with distinct genotype/phenotype characteristics, which deserve further attention with respect to trial interpretation and patient management.

Generation of patient-derived pediatric pilocytic astrocytoma in-vitro models using SV40 large T: evaluation of a modeling workflow

PURPOSE

Although pediatric low-grade gliomas (pLGG) are the most common pediatric brain tumors, patient-derived cell lines reflecting pLGG biology in culture are scarce. This also applies to the most common pLGG subtype pilocytic astrocytoma (PA). Conventional cell culture approaches adapted from higher-grade tumors fail in PA due to oncogene-induced senescence (OIS) driving tumor cells into arrest. Here, we describe a PA modeling workflow using the Simian Virus large T antigen (SV40-TAg) to circumvent OIS.

METHODS

18 pLGG tissue samples (17 (94%) histological and/or molecular diagnosis PA) were mechanically dissociated. Tumor cell positive-selection using A2B5 was perfomed in 8/18 (44%) cases. All primary cell suspensions were seeded in Neural Stem Cell Medium (NSM) and Astrocyte Basal Medium (ABM). Resulting short-term cultures were infected with SV40-TAg lentivirus. Detection of tumor specific alterations (BRAF-duplication and BRAF V600E-mutation) by digital droplet PCR (ddPCR) at defined time points allowed for determination of tumor cell fraction (TCF) and evaluation of the workflow. DNA-methylation profiling and gene-panel sequencing were used for molecular profiling of primary samples.

RESULTS

Primary cell suspensions had a mean TCF of 55% (+/- 23% (SD)). No sample in NSM (0/18) and ten samples in ABM (10/18) were successfully transduced. Three of these ten (30%) converted into long-term pLGG cell lines (TCF 100%), while TCF declined to 0% (outgrowth of microenvironmental cells) in 7/10 (70%) cultures. Young patient age was associated with successful model establishment.

CONCLUSION

A subset of primary PA cultures can be converted into long-term cell lines using SV40-TAg depending on sample intrinsic (patient age) and extrinsic workflow-related (e.g. type of medium, successful transduction) parameters. Careful monitoring of sample-intrinsic and extrinsic factors optimizes the process.

Spontaneous Shrinkage of isocitrate dehydrogenase (IDH)-mutant astrocytoma caused by intra-tumoural cyst rupture: a case report

BACKGROUND

T2-fluid-attenuated inversion recovery (FLAIR) mismatch sign is a specific imaging finding of isocitrate dehydrogenase (IDH)-mutant astrocytomas. Histologically, a hypointense area on FLAIR images indicates the presence of microcysts. Here we report a case of IDH-mutant astrocytoma that shrunk spontaneously.

CASE DESCRIPTION

A 26-year-old woman presented with a complaint of headache. Her magnetic resonance (MR) images revealed a lesion mass with a T2-FLAIR mismatch sign in the left frontal lobe. Subsequently, after 1 month, she was referred to our department, and we found that the lesion had unexpectedly shrunk; however, no further shrinkage was observed in the next 3 months. Furthermore, a biopsy was performed, and the results indicated a diagnosis of astrocytoma, IDH-mutant CNS WHO grade 3. Thus, she underwent subtotal resection. We found no neurological deficits in the patient, and she received 60 Gy of radiotherapy at the local site and chemotherapy with nimustine hydrochloride (ACNU), followed by the administration of ACNU every 8 weeks for 2 years. Overall, after 36 months of tumour resection, she was in good health and exhibited no recurrence. Notably, her histological and MR image findings suggested that the macroscopic cyst was formed by the fusion of microcysts, which is a characteristic feature of IDH-mutant astrocytoma with a T2-FLAIR mismatch sign, and that the tumour shrunk because of the rupture of the cyst in the Sylvian cistern.

CONCLUSION

The present case report suggests that IDH-mutant astrocytoma cannot be ruled out even when the lesion shrinks spontaneously.

Telomere dysfunction in some pediatric congenital and growth-related diseases

Telomere wear and dysfunction may lead to aging-related diseases. Moreover, increasing evidence show that the occurrence, development, and prognosis of some pediatric diseases are also related to telomere dysfunction. In this review, we systematically analyzed the relationship between telomere biology and some pediatric congenital and growth-related diseases and proposed new theoretical basis and therapeutic targets for the treatment of these diseases.

Relationship between telomere length and the prognosis of breast cancer based on estrogen receptor status: A Mendelian randomization study

Objective

To identify the relationship between telomere length and the prognosis of breast cancer with different status of estrogen receptor (ER).

Methods

We collected single nucleotide polymorphisms (SNPs) associated with telomere length and breast cancer prognosis from the MRCIEU GWAS database and the dataset of a large meta-analysis conducted by the Breast Cancer Association Consortium (BCAC), respectively. The relationship was identified using inverse-variance weighted (IVW), MR-Egger, weighted median, penalized weighted median, and maximum likelihood methods. IVW, MR-Egger, and MR-PRESSO methods were used to perform sensitivity analysis to assess the accuracy of the results.

Results

Telomere length was negatively associated with the prognosis of total breast cancer (odds ratio [OR]=1.84, 95% confidence interval [CI]=1.08-3.14, IVW method), especially with ER- breast cancer (OR=1.89, 95% CI=1.11-3.22, IVW method). No similar relationship was found between telomere length and the prognosis of ER+ breast cancer (OR=0.99, 95% CI=0.62-1.58, IVW method). The findings from other methods were consistent with the results shown by the IVW method. The Mendelian randomization assumptions did not appear to be violated. Sensitivity analysis indicated that the result was robust, and no bias was observed in the study.

Conclusion

Telomere length is associated with the prognosis of total breast cancer, especially with ER- breast cancer. There is no significant correlation between telomere length and the prognosis of ER+ breast cancer. These findings add to the evidence that long telomere could predict a poor prognosis of ER- breast cancer.

Pediatric and Adult Low-Grade Gliomas: Where Do the Differences Lie?

Two thirds of pediatric gliomas are classified as low-grade (LGG), while in adults only around 20% of gliomas are low-grade. However, these tumors do not only differ in their incidence but also in their location, behavior and, subsequently, treatment. Pediatric LGG constitute 65% of pilocytic astrocytomas, while in adults the most commonly found histology is diffuse low-grade glioma (WHO II), which mostly occurs in eloquent regions of the brain, while its pediatric counterpart is frequently found in the infratentorial compartment. The different tumor locations require different skillsets from neurosurgeons. In adult LGG, a common practice is awake surgery, which is rarely performed on children. On the other hand, pediatric neurosurgeons are more commonly confronted with infratentorial tumors causing hydrocephalus, which more often require endoscopic or shunt procedures to restore the cerebrospinal fluid flow. In adult and pediatric LGG surgery, gross total excision is the primary treatment strategy. Only tumor recurrences or progression warrant adjuvant therapy with either chemo- or radiotherapy. In pediatric LGG, MEK inhibitors have shown promising initial results in treating recurrent LGG and several ongoing trials are investigating their role and safety. Moreover, predisposition syndromes, such as neurofibromatosis or tuberous sclerosis complex, can increase the risk of developing LGG in children, while in adults, usually no tumor growth in these syndromes is observed. In this review, we discuss and compare the differences between pediatric and adult LGG, emphasizing that pediatric LGG should not be approached and managed in the same way as adult LCG.

Reimagining Pilocytic Astrocytomas in the Context of Pediatric Low-Grade Gliomas

Pediatric low-grade gliomas (pLGGs) are the most common brain tumor in children, and are associated with life-long clinical morbidity. Relative to their high-grade adult counterparts or other malignant childhood brain tumors, there is a paucity of authenticated preclinical models for these pediatric low-grade gliomas and an incomplete understanding of their molecular and cellular pathogenesis. While large scale genomic profiling efforts have identified the majority of pathogenic driver mutations, which converge on the MAPK/ERK signaling pathway, it is now appreciated that these events may not be sufficient by themselves for gliomagenesis and clinical progression. In light of the recent World Health Organization reclassification of pLGGs, and pilocytic astrocytoma (PA) in particular, we review our current understanding of these pediatric brain tumors, provide a conceptual framework for future mechanistic studies, and outline the challenges and pressing needs for the pLGG clinical and research communities.

Adolescent and young adult neuro-oncology: a comprehensive review

Adolescent and young adult (AYA; ages 15-39) patients represent a population that experiences significant challenges in cancer care and research, exemplified by poorer clinical outcomes as well as unmet psychosocial and reproductive health needs. Despite central nervous system (CNS) tumors being one of the most common malignancies diagnosed in the age group, there is a clear paucity of AYA CNS tumor-specific publications, especially those related to the unique psychosocial and reproductive health needs of this population of patients. In this review, we examine various aspects of AYA oncological care including tumor biology, clinical outcome, clinical trials enrollment rate, site of care, unique psychosocial needs, and oncofertility. We assess the current state of these issues, highlight areas of deficiencies, and outline the steps needed to address these concerns. We emphasize the importance of comprehensive molecular testing as part of the diagnostic work-up, expansion of clinical trial availability, access to psychosocial care and oncofertility expertise, and the development of AYA-specific clinical research to define best practices and advancing care for this population.

Trametinib for the treatment of recurrent/progressive pediatric low-grade glioma

PURPOSE

Pediatric low-grade gliomas (pLGGs) are the most common CNS tumor of childhood and comprise a heterogenous group of tumors. Children with progressive pLGG often require numerous treatment modalities including surgery, chemotherapy, rarely radiation therapy and, more recently, molecularly targeted therapy. We describe our institutional experience using the MEK inhibitor, trametinib, for recurrent/progressive pLGGs.

METHODS

We performed a retrospective, IRB-approved, chart review of all pediatric patients treated with trametinib for recurrent/progressive pLGGs at Dana-Farber/Boston Children's Cancer and Blood Disorder Center between 2016 and 2018.

RESULTS

Eleven patients were identified, of which 10 were evaluable for response. Median age at commencement of trametinib treatment was 14.7 years (range 7.3-25.9 years). Tumor molecular status included KIAA1549-BRAF fusion (n = 4), NF1 mutation (n = 4), FGFR mutation (n = 1) and CDKN2A loss (n = 1). Median number of prior treatment regimens was 5 (range 1-12). Median duration of treatment with trametinib was 19.2 months (range 3.8-29.8 months). Based on modified RANO criteria, best responses included partial (n = 2), minor response (n = 2) and stable disease (n = 6). Two patients remain on therapy (29.8 and 25.9 months, respectively). The most common toxicities attributable to trametinib were rash, fatigue and gastrointestinal disturbance. Five patients required dose reduction for toxicities. Two patients experienced significant intracranial hemorrhage (ICH) while on trametinib. While it is unclear whether ICH was directly attributable to trametinib, therapy was discontinued.

CONCLUSION

Trametinib appears to be an effective treatment for patients with recurrent/progressive pLGG. The toxicities of this therapy warrant further investigation, with particular attention to the potential risk for intracranial hemorrhage. Early phase multi-institutional clinical trials are underway.

Efficacy and safety of bevacizumab in progressive pediatric low-grade glioma: a systematic review and meta-analysis of outcome rates

Background

Successful management of pediatric low-grade glioma (pLGG) can be complicated by eloquent anatomical location, as well as specific pathologic and molecular features. Some authors have proposed using the VEGF inhibitor bevacizumab to improve disease control, but its safety and efficacy are poorly defined. Correspondingly, our aim was to pool systematically identified clinical data in the literature to assess the clinical utility of bevacizumab for pLGG at progression.

Methods

A systematic search of 7 electronic databases from inception to June 2019 was conducted following PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) guidelines. Articles were screened against prespecified criteria. Outcomes were then pooled by random-effects meta-analyses of proportions.

Results

Seven pertinent studies described the outcomes of 110 progressive pLGG patients managed with bevacizumab in largely multiagent regimens. While on treatment, the rate of clinical response was 58% (95% CI, 43%-72%), and the rate of response on imaging was 80% (95% CI, 58%-96%). The rate of grade 3 or higher toxicity was 8% (95% CI, 2%-17%), with proteinuria the most commonly described. In the off-treatment period up to median 1 year, the rate of progression was estimated to be 51% (95% CI, 28%-74%).

Conclusions

Bevacizumab has the potential to control clinical and radiographic disease with relatively low grade 3 or higher toxicity risk in progressive pLGG patients. However, the long-term off-treatment benefits of this therapy are not yet well defined. Heterogeneity in the literature precludes any formal recommendations regarding its use until larger, more standardized investigations can be performed.

Telomere Maintenance in Pediatric Cancer

Telomere length has been proposed as a biomarker of biological age and a risk factor for age-related diseases and cancer. Substantial progress has been made in recent decades in understanding the complex molecular relationships in this research field. However, the majority of telomere studies have been conducted in adults. The data on telomere dynamics in pediatric cancers is limited, and interpretation can be challenging, especially in cases where results are contrasting to those in adult entities. This review describes recent advances in the molecular characterization of structure and function of telomeres, regulation of telomerase activity in cancer pathogenesis in general, and highlights the key advances that have expanded our views on telomere biology in pediatric cancer, with special emphasis on the central role of telomere maintenance in neuroblastoma. Furthermore, open questions in the field of telomere maintenance research are discussed in the context of recently published literature.

Stilbene Compounds Inhibit Tumor Growth by the Induction of Cellular Senescence and the Inhibition of Telomerase Activity

Cellular senescence is a state of cell cycle arrest characterized by a distinct morphology, gene expression pattern, and secretory phenotype. It can be triggered by multiple mechanisms, including those involved in telomere shortening, the accumulation of DNA damage, epigenetic pathways, and the senescence-associated secretory phenotype (SASP), and so on. In current cancer therapy, cellular senescence has emerged as a potent tumor suppression mechanism that restrains proliferation in cells at risk for malignant transformation. Therefore, compounds that stimulate the growth inhibition effects of senescence while limiting its detrimental effects are believed to have great clinical potential. In this review article, we first review the current knowledge of the pro- and antitumorigeneic functions of senescence and summarize the key roles of telomerase in the regulation of senescence in tumors. Second, we review the current literature regarding the anticancer effects of stilbene compounds that are mediated by the targeting of telomerase and cell senescence. Finally, we provide future perspectives on the clinical utilization of stilbene compounds, especially resveratrol and pterostilbene, as novel cancer therapeutic remedies. We conclude and propose that stilbene compounds may induce senescence and may potentially be used as the therapeutic or adjuvant agents for cancers with high telomerase activity.

Combined genetic and epigenetic alterations of the TERT promoter affect clinical and biological behavior of bladder cancer

In urothelial bladder cancer (UBC), risk stratification remains an important unmet need. Limitless self‐renewal, governed by TERT expression and telomerase activation, is crucial for cancer progression. Thus, telomerase activation through the interplay of mutations (TERTp^Mut) and epigenetic alterations in the TERT promoter may provide further insight into UBC behavior. Here, we investigated the combined effect of TERTp^Mut and the TERT Hypermethylated Oncological Region (THOR) status on telomerase activation and patient outcome in a UBC international cohort (n = 237). We verified that TERTp^Mut were frequent (76.8%) and present in all stages and grades of UBC. Hypermethylation of THOR was associated with higher TERT expression and higher‐risk disease in nonmuscle invasive bladder cancers (NMIBC). TERTp^Mut alone predicted disease recurrence (HR: 3.18, 95%CI 1.84 to 5.51, p < 0.0001) but not progression in NMIBC. Combined THOR^high/TERTp^Mut increased the risk of disease recurrence (HR 5.12, p < 0.0001) and progression (HR 3.92, p = 0.025). Increased THOR hypermethylation doubled the risk of stage progression of both TERTp^wt and TERTp^Mut NMIBC. These results highlight that both mechanisms are common and coexist in bladder cancer and while TERTp^Mut is an early event in bladder carcinogenesis THOR hypermethylation is a dynamic process that contributes to disease progression. While the absence of alterations comprises an extremely indolent phenotype, the combined genetic and epigenetic alterations of TERT bring additional prognostic value in NMIBC and provide a novel insight into telomere biology in cancer.

What's new?

Telomerase reverse transcriptase (TERT) activation is central to cancer cell immortalization. It acts, however, through relatively unknown mechanisms. In urothelial bladder cancer (UBC) in particular, TERT activation can occur in the presence or absence of mutation, raising questions about alternative activation mechanisms. Our study shows that hypermethylation of the TERT promoter (THOR) plays a key part in UBC, being a dynamic and progressive process, with hypermethylation levels increasing with bladder cancer severity. Moreover, both hypermethylation and TERT promoter mutation contributed to increased telomerase expression. The findings provide insight into telomere biology in UBC and may be applicable to other tumors.

Establishment of primary cell culture and an intracranial xenograft model of pediatric ependymoma: a prospect for therapy development and understanding of tumor biology

Background

Ependymoma (EPN), the third most common pediatric brain tumor, is a central nervous system (CNS) malignancy originating from the walls of the ventricular system. Surgical resection followed by radiation therapy has been the primary treatment for most pediatric intracranial EPNs. Despite numerous studies into the prognostic value of histological classification, the extent of surgical resection and adjuvant radiotherapy, there have been relatively few studies into the molecular and cellular biology of EPNs.

Results

We elucidated the ultrastructure of the cultured EPN cells and characterized their profile of immunophenotypic pluripotency markers (CD133, CD90, SSEA-3, CXCR4). We established an experimental EPN model by the intracerebroventricular infusion of EPN cells labeled with multimodal iron oxide nanoparticles (MION), thereby generating a tumor and providing a clinically relevant animal model. MRI analysis was shown to be a valuable tool when combined with effective MION labeling techniques to accompany EPN growth.

Conclusions

We demonstrated that GFAP/CD133+CD90+/CD44+ EPN cells maintained key histopathological and growth characteristics of the original patient tumor. The characterization of EPN cells and the experimental model could facilitate biological studies and preclinical drug screening for pediatric EPNs.

Methods

In this work, we established notoriously challenging primary cell culture of anaplastic EPNs (WHO grade III) localized in the posterior fossa (PF), using EPNs obtained from 1 to 10-year-old patients (n = 07), and then characterized their immunophenotype and ultrastructure to finally develop a xenograft model.

Mortality in children with low-grade glioma or glioneuronal tumors: A single-institution study

BACKGROUND

While pediatric low-grade glioma/glioneuronal tumors (LGG/LGGNTs) are considered slow-growing, indolent tumors with excellent long-term prognosis, mortality due to the disease is not unknown. Few studies have addressed the cause of death in this population.

METHODS

Retrospective review of clinicopathologic and radiologic data for children 21 years or younger with LGG/LGGNT who died at St. Jude Children's Research Hospital between April 1985 and June 2015. Our primary objective was to determine the causes and timing of mortality in affected children.

RESULTS

For the 87 eligible patients, median age at diagnosis was 7.7 years (range, 0.21-21 years), median age at death was 14.26 years (range, 0.58-32 years), and median time to death from diagnosis was 4.02 years (range, 0.21-24 years). Midbrain/thalamus was the most common tumor location (n = 34), followed by suprasellar/hypothalamic (n = 18) and cerebrocortical (n = 13). Astrocytoma not otherwise specified (n = 24), pilocytic astrocytoma (n = 23), and fibrillary astrocytoma (n = 11) were the predominant histologic diagnoses. Causes of death included progressive primary disease (PD) (n = 43), progression of PD with histological features of a high-grade glioma at progression or at autopsy (PD-HGG) (n = 15), second cancer (n = 3), suicide (n = 4), and vehicular accident (n = 3). Among the 15 patients with PD-HGG, 12 received radiation therapy before histologic confirmation of progression.

CONCLUSIONS

PD and PD-HGG contributed to 66% of the mortality in our patient cohort. Early psychological intervention should be included as part of the multidisciplinary management approach of children with LGG/LGGNT to reduce the risk of suicide in vulnerable subjects.

Establishment and application of a novel patient-derived KIAA1549:BRAF-driven pediatric pilocytic astrocytoma model for preclinical drug testing

Pilocytic astrocytoma (PA) is the most frequent pediatric brain tumor. Activation of the MAPK pathway is well established as the oncogenic driver of the disease. It is most frequently caused by KIAA1549:BRAF fusions, and leads to oncogene induced senescence (OIS). OIS is thought to be a major reason for growth arrest of PA cells in vitro and in vivo, preventing establishment of PA cultures. Hence, valid preclinical models are currently very limited, but preclinical testing of new compounds is urgently needed. We transduced the PA short-term culture DKFZ-BT66 derived from the PA of a 2-year old patient with a doxycycline-inducible system coding for Simian Vacuolating Virus 40 Large T Antigen (SV40-TAg). SV40-TAg inhibits TP53/CDKN1A and CDKN2A/RB1, two pathways critical for OIS induction and maintenance. DNA methylation array and KIAA1549:BRAF fusion analysis confirmed pilocytic astrocytoma identity of DKFZ-BT66 cells after establishment. Readouts were analyzed in proliferating as well as senescent states, including cell counts, viability, cell cycle analysis, expression of SV40-Tag, CDKN2A (p16), CDKN1A (p21), and TP53 (p53) protein, and gene-expression profiling. Selected MAPK inhibitors (MAPKi) including clinically available MEK inhibitors (MEKi) were tested in vitro. Expression of SV40-TAg enabled the cells to bypass OIS and to resume proliferation with a mean doubling time of 45h allowing for propagation and long-term culture. Withdrawal of doxycycline led to an immediate decrease of SV40-TAg expression, appearance of senescent morphology, upregulation of CDKI proteins and a subsequent G1 growth arrest in line with the re-induction of senescence. DKFZ-BT66 cells still underwent replicative senescence that was overcome by TERT expression. Testing of a set of MAPKi revealed differential responses in DKFZ-BT66. MEKi efficiently inhibited MAPK signaling at clinically achievable concentrations, while BRAF V600E- and RAF Type II inhibitors showed paradoxical activation. Taken together, we have established the first patient-derived long term expandable PA cell line expressing the KIAA1549:BRAF-fusion suitable for preclinical drug testing.

Phase II Weekly Vinblastine for Chemotherapy-Naïve Children With Progressive Low-Grade Glioma: A Canadian Pediatric Brain Tumor Consortium Study

Purpose Vinblastine monotherapy has shown promising activity and a low-toxicity profile in patients with pediatric low-grade glioma (PLGG) who experienced treatment failure after initial treatment with chemotherapy and/or radiation. The aim of this study was to assess the activity of vinblastine in therapy-naïve children. Patients and Methods Patients < 18 years old with unresectable and/or progressive therapy-naïve PLGG were eligible. Vinblastine was administered once per week at a dose of 6 mg/m² intravenously over a period of 70 weeks. Vision, quality of life, neurofibromatosis type 1 (NF1) status, and BRAF mutation/fusion status were also determined and correlated with outcome. Results Fifty-four patients were enrolled onto the study, with a median age of 8 years (range, 0.7 to 17.2 years). Most patients had chiasmatic/hypothalamic tumors (55.5%), and 13 patients (24.1%) had NF1. The most common histology was pilocytic astrocytoma (46.3%). Seventeen patients were diagnosed using radiologic criteria alone. Best response to chemotherapy was centrally reviewed with a response rate (complete, partial, or minor response) of 25.9%. Disease stabilization (complete, partial, or minor response or stable disease) was achieved in 47 patients (87.0%). Visual improvement was observed in 20% of patients with optic pathway glioma. Five-year overall survival and progression-free survival (PFS) rates were 94.4% (95% CI, 88.5% to 100%) and 53.2% (95% CI, 41.3% to 68.5%), respectively, for the entire cohort. Patients with NF1 had a significantly better PFS (85.1%; 95% CI, 68.0% to 100%) when compared with patients without NF1 (42.0%; 95% CI, 29.1% to 60.7%; P = .012). Age< 3 years or > 10 years was not associated with poor outcome. Treatment was well tolerated, and quality of life was not affected during treatment. In this trial, there was no correlation between BRAF alterations and outcome. Conclusion Vinblastine administered once per week is well tolerated in children with treatment naïve PLGG. Overall survival and PFS are comparable to current therapies, with a favorable toxicity profile and a maintained quality of life.

The role of histone modifications and telomere alterations in the pathogenesis of diffuse gliomas in adults and children

Genetic profiling is an increasingly useful tool for sub-classification of gliomas in adults and children. Specific gene mutations, structural rearrangements, DNA methylation patterns, and gene expression profiles are now recognized to define molecular subgroups of gliomas that arise in distinct anatomic locations and patient age groups, and also provide a better prediction of clinical outcomes for glioma patients compared to histologic assessment alone. Understanding the role of these distinctive genetic alterations in gliomagenesis is also important for the development of potential targeted therapeutic interventions. Mutations including K27M and G34R/V that affect critical amino acids within the N-terminal tail of the histone H3 variants, H3.3 and H3.1 (encoded by H3F3A and HIST1H3B genes), are prime examples of mutations in diffuse gliomas with characteristic clinical associations that can help diagnostic classification and guide effective patient management. These histone H3 mutations frequently co-occur with inactivating mutations in ATRX in association with alternative lengthening of telomeres. Telomere length can also be maintained through upregulation of telomerase reverse transcriptase (TERT) expression driven by mutation within the TERT gene promoter region, an alteration most commonly found in oligodendrogliomas and primary glioblastomas arising in adults. Interestingly, the genetic alterations perturbing histone and telomere function in pediatric gliomas tend to be different from those present in adult tumors. We present a review of these mutations affecting the histone code and telomere length, highlighting their importance in prognosis and as targets for novel therapeutics in the treatment of diffuse gliomas.

Life and cancer without telomerase: ALT and other strategies for making sure ends (don't) meet

While most cancer cells rely on telomerase expression/re-activation for linear chromosome maintenance and sustained proliferation, a significant population of cancers (10-15%) employs telomerase-independent strategies, collectively dubbed Alternative Lengthening of Telomeres (ALT). Most ALT cells relax the usual role of telomeres as inhibitors of local homologous recombination while maintaining the ability of telomeres to prohibit local non-homologous end joining reactions. Here we review current concepts surrounding how ALT telomeres achieve this new balance via alterations in chromatin landscape, DNA damage repair processes and handling of telomeric transcription. We also discuss telomerase independent end maintenance strategies utilized by other organisms, including fruitflies and yeasts, to draw parallels and contrasts and highlight additional modes, beyond ALT, that may be available to telomerase-minus cancers. We conclude by commenting on promises and challenges in the development of effective anti-ALT cancer therapies.

Endoscopic third ventriculostomy for hydrocephalus due to tectal glioma

BACKGROUND

Tectal gliomas commonly present with hydrocephalus from obstruction of the aqueduct of Sylvius. The creation of a ventriculostomy in the floor of the third ventricle (ETV) has been previously reported to by-pass aqueduct obstruction. The goal of this study was to determine the safety and efficacy of ETV in the presence of an obstructing tectal glioma.

METHODS

We retrospectively reviewed the clinical presentation, management, and clinical outcome after ETV in patients diagnosed with tectal glioma and obstructive hydrocephalus in our institution over a period of 15 years. Shunt freedom at follow-up was the main outcome variable. Long-term clinical outcome was assessed at the most recent clinic visit. Clinical outcome was ranked as excellent, good, or poor according to resolution of symptoms and patient functional status.

RESULTS

The median age at presentation was 16.5 years (range: 6.4 to 59 years) and the most common presenting symptom was headache. Eleven patients had ETV as a primary procedure and three patients underwent ETV as a substitute for shunt revision at the time of shunt failure. At follow-up (median 3.9 years, range: 2.2 to 7 years) 13 of 14 patients remain shunt independent with excellent (n=9) or good outcomes (n=5).

CONCLUSIONS

In patients with tectal glioma causing obstructive hydrocephalus, ETV can be performed safely in the primary setting or as a substitute for shunt revision. A high rate of shunt freedom (78%-100%) at prolonged follow-up can be expected in this patient population.

Role of Telomeres and Telomerase in Aging and Cancer

Telomeres progressively shorten throughout life. A hallmark of advanced malignancies is the ability for continuous cell divisions that almost universally correlates with the stabilization of telomere length by the reactivation of telomerase. The repression of telomerase and shorter telomeres in humans may have evolved, in part, as an anticancer protection mechanism. Although there is still much we do not understand about the regulation of telomerase, it remains a very attractive and novel target for cancer therapeutics. This review focuses on the current state of advances in the telomerase area, identifies outstanding questions, and addresses areas and methods that need refinement.

SIGNIFICANCE

Despite many recent advances, telomerase remains a challenging target for cancer therapy. There are few telomerase-directed therapies, and many of the assays used to measure telomeres and telomerase have serious limitations. This review provides an overview of the current state of the field and how recent advances could affect future research and treatment approaches. Cancer Discov; 6(6); 584-93. ©2016 AACR.

Telomere profiles and tumor-associated macrophages with different immune signatures affect prognosis in glioblastoma

Telomere maintenance is a hallmark of cancer and likely to be targeted in future treatments. In glioblastoma established methods of identifying telomerase and alternative lengthening of telomeres leave a significant proportion of tumors with no defined telomere maintenance mechanism. This study investigated the composition of these tumors using RNA-Seq. Glioblastomas with an indeterminate telomere maintenance mechanism had an increased immune signature compared with alternative lengthening of telomeres and telomerase-positive tumors. Immunohistochemistry for CD163 confirmed that the majority (80%) of tumors with an indeterminate telomere maintenance mechanism had a high presence of tumor-associated macrophages. The RNA-Seq and immunostaining data separated tumors with no defined telomere maintenance mechanism into three subgroups: alternative lengthening of telomeres like tumors with a high presence of tumor-associated macrophages and telomerase like tumors with a high presence of tumor-associated macrophages. The third subgroup had no increase in tumor-associated macrophages and may represent a distinct category. The presence of tumor-associated macrophages conferred a worse prognosis with reduced patient survival times (alternative lengthening of telomeres with and without macrophages P=0.0004, and telomerase with and without macrophages P=0.013). The immune signatures obtained from RNA-Seq were significantly different between telomere maintenance mechanisms. Alternative lengthening of telomeres like tumors with macrophages had increased expression of interferon-induced proteins with tetratricopeptide repeats (IFIT1-3). Telomerase-positive tumors with macrophages had increased expression of macrophage receptor with collagenous structure (MARCO), CXCL12 and sushi-repeat containing protein x-linked 2 (SRPX2). Telomerase-positive tumors with macrophages were also associated with a reduced frequency of total/near total resections (44% vs >76% for all other subtypes, P=0.014). In summary, different immune signatures are found among telomere maintenance mechanism-based subgroups in glioblastoma. The reduced extent of surgical resection of telomerase-positive tumors with macrophages suggests that some tumor-associated macrophages are more unfavorable.

Expression profiles of 151 pediatric low-grade gliomas reveal molecular differences associated with location and histological subtype

BACKGROUND

Pediatric low-grade gliomas (PLGGs), the most frequent pediatric brain tumor, comprise a heterogeneous group of diseases. Recent genomic analyses suggest that these tumors are mostly driven by mitogene-activated protein kinase (MAPK) pathway alterations. However, little is known about the molecular characteristics inherent to their clinical and histological heterogeneity.

METHODS

We performed gene expression profiling on 151 paraffin-embedded PLGGs from different locations, ages, and histologies. Using unsupervised and supervised analyses, we compared molecular features with age, location, histology, and BRAF genomic status. We compared molecular differences with normal pediatric brain expression profiles to observe whether those patterns were mirrored in normal brain.

RESULTS

Unsupervised clustering distinguished 3 molecular groups that correlated with location in the brain and histological subtype. "Not otherwise specified" (NOS) tumors did not constitute a unified class. Supratentorial pilocytic astrocytomas (PAs) were significantly enriched with genes involved in pathways related to inflammatory activity compared with infratentorial tumors. Differences based on tumor location were not mirrored in location-dependent differences in expression within normal brain tissue. We identified significant differences between supratentorial PAs and diffuse astrocytomas as well as between supratentorial PAs and dysembryoplastic neuroepithelial tumors but not between supratentorial PAs and gangliogliomas. Similar expression patterns were observed between childhood and adolescent PAs. We identified differences between BRAF-duplicated and V600E-mutated tumors but not between primary and recurrent PLGGs.

CONCLUSION

Expression profiling of PLGGs reveals significant differences associated with tumor location, histology, and BRAF genomic status. Supratentorial PAs, in particular, are enriched in inflammatory pathways that appear to be tumor-related.

Telomerase inhibition abolishes the tumorigenicity of pediatric ependymoma tumor-initiating cells

Pediatric ependymomas are highly recurrent tumors resistant to conventional chemotherapy. Telomerase, a ribonucleoprotein critical in permitting limitless replication, has been found to be critically important for the maintenance of tumor-initiating cells (TICs). These TICs are chemoresistant, repopulate the tumor from which they are identified, and are drivers of recurrence in numerous cancers. In this study, telomerase enzymatic activity was directly measured and inhibited to assess the therapeutic potential of targeting telomerase. Telomerase repeat amplification protocol (TRAP) (n = 36) and C-circle assay/telomere FISH/ATRX staining (n = 76) were performed on primary ependymomas to determine the prevalence and prognostic potential of telomerase activity or alternative lengthening of telomeres (ALT) as telomere maintenance mechanisms, respectively. Imetelstat, a phase 2 telomerase inhibitor, was used to elucidate the effect of telomerase inhibition on proliferation and tumorigenicity in established cell lines (BXD-1425EPN, R254), a primary TIC line (E520) and xenograft models of pediatric ependymoma. Over 60 % of pediatric ependymomas were found to rely on telomerase activity to maintain telomeres, while no ependymomas showed evidence of ALT. Children with telomerase-active tumors had reduced 5-year progression-free survival (29 ± 11 vs 64 ± 18 %; p = 0.03) and overall survival (58 ± 12 vs 83 ± 15 %; p = 0.05) rates compared to those with tumors lacking telomerase activity. Imetelstat inhibited proliferation and self-renewal by shortening telomeres and inducing senescence in vitro. In vivo, Imetelstat significantly reduced subcutaneous xenograft growth by 40 % (p = 0.03) and completely abolished the tumorigenicity of pediatric ependymoma TICs in an orthotopic xenograft model. Telomerase inhibition represents a promising therapeutic approach for telomerase-active pediatric ependymomas found to characterize high-risk ependymomas.

Alternative lengthening of telomeres is enriched in, and impacts survival of TP53 mutant pediatric malignant brain tumors

Although telomeres are maintained in most cancers by telomerase activation, a subset of tumors utilize alternative lengthening of telomeres (ALT) to sustain self-renewal capacity. In order to study the prevalence and significance of ALT in childhood brain tumors we screened 517 pediatric brain tumors using the novel C-circle assay. We examined the association of ALT with alterations in genes found to segregate with specific histological phenotypes and with clinical outcome. ALT was detected almost exclusively in malignant tumors (p = 0.001). ALT was highly enriched in primitive neuroectodermal tumors (12 %), choroid plexus carcinomas (23 %) and high-grade gliomas (22 %). Furthermore, in contrast to adult gliomas, pediatric low grade gliomas which progressed to high-grade tumors did not exhibit the ALT phenotype. Somatic but not germline TP53 mutations were highly associated with ALT (p = 1.01 × 10(-8)). Of the other alterations examined, only ATRX point mutations and reduced expression were associated with the ALT phenotype (p = 0.0005). Interestingly, ALT attenuated the poor outcome conferred by TP53 mutations in specific pediatric brain tumors. Due to very poor prognosis, one year overall survival was quantified in malignant gliomas, while in children with choroid plexus carcinoma, five year overall survival was investigated. For children with TP53 mutant malignant gliomas, one year overall survival was 63 ± 12 and 23 ± 10 % for ALT positive and negative tumors, respectively (p = 0.03), while for children with TP53 mutant choroid plexus carcinomas, 5 years overall survival was 67 ± 19 and 27 ± 13 % for ALT positive and negative tumors, respectively (p = 0.07). These observations suggest that the presence of ALT is limited to a specific group of childhood brain cancers which harbor somatic TP53 mutations and may influence the outcome of these patients. Analysis of ALT may contribute to risk stratification and targeted therapies to improve outcome for these children.

Are short telomeres hallmarks of cancer recurrence?

Exposure to radiation and some chemotherapeutic agents is associated with an increased risk of developing second cancers. Short telomeres are almost universally associated with malignant cancer progression. An unanswered question is whether inherited short telomeres or therapy-related telomere shortening is a biomarker of the development of second malignant neoplasms.

Study of chromosome 9q gain, Notch pathway regulators and Tenascin-C in ependymomas

Ependymomas are relatively uncommon tumours of the central nervous system which arise from the ependymal lining of the ventricles and spinal canal. The molecular changes leading to ependymal oncogenesis are not completely understood. We examined chromosome 9q33-34 locus for gain, potential oncogenes at this locus (Notch-1 and Tenascin-C) and Notch pathway target genes (Hes-1, Hey-2 & C-myc) in ependymomas by fluorescent in situ hybridization (FISH) and immunohistochemistry (IHC), respectively, to assess if they have any correlation with clinical characteristics. We analyzed 50 cases of ependymomas by FISH for 9q gain and by IHC for Notch-1 and its target gene proteins (Hes-1, Hey-2 and C-myc) expression. We also performed IHC for Tenascin-C to rule out any correlation with aggressiveness/grade of tumour. FISH study revealed significant chromosome 9q gain in ependymomas of adult onset (age > 18 years) and spinal cord origin. Notch-1 showed significantly more frequent immunohistochemical expression in supratentorial and anaplastic ependymomas. Tenascin-C (TN-C) expression was significant in intracranial, childhood (age ≤ 18 years) and anaplastic ependymomas. Of the three Notch pathway target gene proteins (Hes-1, Hey-2 and C-myc), Hes-1 and C-myc expression showed significant correlation with anaplastic and adult onset ependymomas, respectively. Genetic alterations are independent prognostic markers in ependymomas. A clinicopathological correlation with various molecular signatures may be helpful in the development of new therapeutic targets.

Long-term efficacy and toxicity of bevacizumab-based therapy in children with recurrent low-grade gliomas

BACKGROUND

Because definitive resection or radiotherapy for pediatric low-grade gliomas (LGGs) may be associated with severe and permanent adverse effects, medical management has taken a significant role. Bevacizumab-based therapy has demonstrated encouraging responses; however, longer-term toxicity, response durability and alternative dosing regimens have not been evaluated.

PROCEDURE

This was a retrospective review of children with multiply recurrent, progressive LGGs treated with bevacizumab-based therapy and followed for at least 12 months after treatment completion. Toxicity was uniformly graded and imaging was centrally reviewed.

RESULTS

All fourteen patients had failed at least two prior treatment regimens; six had dissemination. Patients received initial bevacizumab-based therapy at a median age of 5.3 years (range, 1-12 years). Median treatment duration was 12 months (range, 1-24 months). 12 patients had an objective response; 2 had stable disease. Median time to maximum response was 9 weeks (range, 7-17 weeks). No patients progressed on therapy, although 13/14 progressed after stopping bevacizumab at a median of 5 months. Four patients were re-treated with bevacizumab and all again responded or stabilized. Alternative dosing strategies were effective, including bevacizumab monotherapy and prolonging the dosing interval to 3 weeks. High-grade bevacizumab-related toxicities consisted of grade 3 proteinuria (n = 2), primary inflammatory arthritis (n = 1), and somnolence (n = 1). Toxicities resolved within 6 months of treatment cessation except one case of hypertension.

CONCLUSIONS

Bevacizumab-based therapy is successful at inducing rapid LGG response. Patients progressing off-therapy may be successfully re-treated with bevacizumab. Nearly all tumors progress once treatment is discontinued. Toxicities are not insignificant but usually reversible.

Methylation of the TERT promoter and risk stratification of childhood brain tumours: an integrative genomic and molecular study

BACKGROUND

Identification of robust biomarkers of malignancy and methods to establish disease progression is a major goal in paediatric neuro-oncology. We investigated whether methylation of the TERT promoter can be a biomarker for malignancy and patient outcome in paediatric brain tumours.

METHODS

For the discovery cohort, we used samples obtained from patients with paediatric brain tumours and individuals with normal brain tissues stored at the German Cancer Research Center (Heidelberg, Germany). We used methylation arrays for genome-wide assessment of DNA. For the validation cohort, we used samples obtained from several tissues for which full clinical and follow-up data were available from two hospitals in Toronto (ON, Canada). We did methylation analysis using quantitative Sequenom and pyrosequencing of an identified region of the TERT promoter. We assessed TERT expression by real-time PCR. To establish whether the biomarker could be used to assess and predict progression, we analysed methylation in paired samples of tumours that transformed from low to high grade and from localised to metastatic, and in choroid plexus tumours of different grades. Finally, we investigated overall survival in patients with posterior fossa ependymomas in which the identified region was hypermethylated or not. All individuals responsible for assays were masked to the outcome of the patients.

FINDINGS

Analysis of 280 samples in the discovery cohort identified one CpG site (cg11625005) in which 78 (99%) of 79 samples from normal brain tissues and low-grade tumours were not hypermethylated, but 145 (72%) of 201 samples from malignant tumours were hypermethylated (>15% methylated; p<0.0001). Analysis of 68 samples in the validation cohort identified a subset of five CpG sites (henceforth, upstream of the transcription start site [UTSS]) that was hypermethylated in all malignant paediatric brain tumours that expressed TERT but not in normal tissues that did not express TERT (p<0.0001). UTSS had a positive predictive value of 1.00 (95% CI 0.95-1.00) and a negative predictive value of 0.95 (0.87-0.99). In two paired samples of paediatric gliomas, UTSS methylation increased during transformation from low to high grade; it also increased in two paired samples that progressed from localised to metastatic disease. Two of eight atypical papillomas that had high UTSS methylation progressed to carcinomas, while the other six assessed did not progress or require additional treatment. 5-year overall survival was 51% (95% CI 31-71) for 25 patients with hypermethylated UTSS posterior fossa ependymomas and 95% (86-100) for 20 with non-hypermethylated tumours (p=0.0008). 5-year progression-free survival was 86% (68-100) for the 25 patients with non-hypermethylated UTSS tumours and 30% (10-50) for those with hypermethylated tumours (p=0.0008).

INTERPRETATION

Hypermethylation of the UTSS region in the TERT promoter is associated with TERT expression in cancers. In paediatric brain tumours, UTSS hypermethylation is associated with tumour progression and poor prognosis. This region is easy to amplify, and the assay to establish hypermethylation can be done on most tissues in most clinical laboratories. Therefore the UTSS region is a potentially accessible biomarker for various cancers.

FUNDING

The Canadian Institute of Health Research and the Terry Fox Foundation.

Central nervous system tumors

Central nervous system tumors are the most frequent malignant tumor in children and the main cause of death in this age group after traffic accidents. The current estimates are that one adult in 2500 is a survivor of a brain tumor that occurred during childhood. These tumors are particularly heterogeneous in terms of histology/biology, treatment, and outcome. They share, however, a high risk of neurological and cognitive morbidity due to the disease itself and the treatment modalities (radiotherapy, surgery, and chemotherapy). Diagnosis is frequently delayed because symptoms are usually nonspecific at the beginning of the evolution. Posterior fossa is the most frequent site and the tumors present most frequently with signs of intracranial hypertension. Supratentorial tumors are more frequent in infants and in adolescents; seizures are not uncommon, especially for benign tumors. When adjuvant treatment is needed, radiotherapy is usually the mainstay apart from some histologies where chemotherapy may be sufficient: low-grade gliomas, desmoplastic medulloblastomas, malignant glial tumors in infants. Multidisciplinary care is best performed in tertiary care centers and should include early rehabilitation programs soon after surgery.

Pathological and molecular advances in pediatric low-grade astrocytoma

Pediatric low-grade astrocytomas are the most common brain tumors in children. They can have similar microscopic and clinical features, making accurate diagnosis difficult. For patients whose tumors are in locations that do not permit full resection, or those with an intrinsically aggressive biology, more effective therapies are required. Until recently, little was known about the molecular changes that drive the initiation and growth of pilocytic and other low-grade astrocytomas beyond the association of a minority of cases, primarily in the optic nerve, with neurofibromatosis type 1. Over the past several years, a wide range of studies have implicated the BRAF oncogene and other members of this signaling cascade in the pathobiology of pediatric low-grade astrocytoma. In this review, we attempt to summarize this rapidly developing field and discuss the potential for translating our growing molecular knowledge into improved diagnostic and prognostic biomarkers and new targeted therapies.

Malignant transformation in pediatric spinal intramedullary tumors: case-based update

BACKGROUND

In children, intramedullary spinal cord neoplasms are rare. These are typically low-grade neuroepithelial tumors, most commonly astrocytomas, ependymomas, and gangliogliomas. Malignant transformation, while common in recurrent adult low-grade gliomas, is an unusual event in pediatric low-grade neoplasms, specifically in intramedullary spinal cord tumors.

ILLUSTRATIVE CASES

We report two cases of malignant transformation in low-grade neuroepithelial tumors of the pediatric intramedullary spinal cord. Two children with intramedullary tumors, one with a WHO grade I ganglioglioma and one with a low-grade astrocytoma, were treated surgically, diagnosed histologically, and followed through the course of their disease. Both patients' tumors transformed to higher grades without prior irradiation or chemotherapy, and without a genetic predisposition to tumorigenesis.

DISCUSSION

Malignant transformation can occur in low-grade intramedullary neoplasms in children. This is a novel documented event for pediatric intramedullary spinal cord tumors and a rare event for all pediatric low-grade neuroepithelial tumors without induction by irradiation. A survey of the relevant literature reveals an underwhelming number of studies focusing on malignant transformation in children's CNS tumors relative to adults. Further investigation into molecular mechanisms of pediatric low-grade neoplasms may reveal more aggressive tumor sub-variants predisposed to malignant degeneration.

Spontaneous regression of pancreatic cancer: Real or a misdiagnosis?

Spontaneous tumor regression has been subject of numerous studies and speculations for many years. This phenomenon is exceptional, but well reported, in some types of tumors, but not in pancreatic cancer. Pancreatic cancer has the worst five-year survival rate of any cancer. Despite numerous molecular studies and clinical approaches, using several mouse models, this cancer responds poorly to the existing chemotherapeutic agents and progress on treatment remains elusive. Although pancreatic cancer tumors seldom undergo spontaneous regression, and some authors take that with skepticism, there are some cases reported in the literature. However, the variability in the description of the reports and technical details could make this process susceptible to misdiagnosis. Distinguishing between different types of pancreatic carcinoma should be taken with caution as they have wide differences in malignant potential. Diseases such as pancreatic benign tumors, insulinomas, or autoimmune pancreatitis could be responsible for this misdiagnosis as a pancreatic cancer. Here we review different cases reported, their clinical characteristics, and possible mechanisms leading to spontaneous regression of pancreatic cancer. We also discuss the possibilities of misdiagnosis.

BRAF activation induces transformation and then senescence in human neural stem cells: a pilocytic astrocytoma model

PURPOSE

BRAF is frequently activated by gene fusion or point mutation in pilocytic astrocytoma, the most common pediatric brain tumor. We investigated the functional effect of constitutive BRAF activation in normal human neural stem and progenitor cells to determine its role in tumor induction in the brain.

EXPERIMENTAL DESIGN

The constitutively active BRAF(V600E) allele was introduced into human neurospheres, and its effects on MAPK (mitogen-activated protein kinase) signaling, proliferation, soft agarose colony formation, stem cell phenotype, and induction of cellular senescence were assayed. Immunohistochemistry was used to examine p16(INK4a) levels in pilocytic astrocytoma.

RESULTS

BRAF(V600E) expression initially strongly promoted colony formation but did not lead to significantly increased proliferation. BRAF(V600E)-expressing cells subsequently stopped proliferating and induced markers of oncogene-induced senescence including acidic β-galactosidase, PAI-1, and p16(INK4a) whereas controls did not. Onset of senescence was associated with decreased expression of neural stem cell markers including SOX2. Primary pilocytic astrocytoma cultures also showed induction of acidic β-galactosidase activity. Immunohistochemical examination of 66 pilocytic astrocytomas revealed p16(INK4a) immunoreactivity in the majority of cases, but patients with tumors negative for p16(INK4a) had significantly shorter overall survival.

CONCLUSIONS

BRAF activation in human neural stem and progenitor cells initially promotes clonogenic growth in soft agarose, suggesting partial cellular transformation, but oncogene-induced senescence subsequently limits proliferation. Induction of senescence by BRAF may help explain the low-grade pathobiology of pilocytic astrocytoma, whereas worse clinical outcomes associated with tumors lacking p16(INK4a) expression could reflect failure to induce senescence or an escape from oncogene-induced senescence.

Neural tumor-initiating cells have distinct telomere maintenance and can be safely targeted for telomerase inhibition

PURPOSE

Cancer recurrence is one of the major setbacks in oncology. Maintaining telomeres is essential for sustaining the limitless replicative potential of such cancers. Because telomerase is thought to be active in all tumor cells and normal stem cells, telomerase inhibition may be nonspecific and have detrimental effects on tissue maintenance and development by affecting normal stem cell self-renewal.

METHODS

We examined telomerase activity, telomere maintenance, and stem cell maturation in tumor subpopulations from freshly resected gliomas, long-term, primary, neural tumor-initiating cells (TIC) and corresponding normal stem cell lines. We then tested the efficacy of the telomerase inhibitor Imetelstat on propagation and self-renewal capacity of TIC and normal stem cells in vitro and in vivo.

RESULTS

Telomerase was undetectable in the majority of tumor cells and specific to the TIC subpopulation that possessed critically short telomeres. In contrast, normal tissue stem cells had longer telomeres and undetectable telomerase activity and were insensitive to telomerase inhibition, which results in proliferation arrest, cell maturation, and DNA damage in neural TIC. Significant survival benefit and late tumor growth arrest of neuroblastoma TIC were observed in a xenograft model (P = 0.02). Furthermore, neural TIC exhibited irreversible loss of self-renewal and stem cell capabilities even after cessation of treatment in vitro and in vivo.

CONCLUSIONS

TIC exhaustion with telomerase inhibition and lack of telomerase dependency in normal stem cells add new dimensions to the telomere hypothesis and suggest that targeting TIC with telomerase inhibitors may represent a specific and safe therapeutic approach for tumors of neural origin.

The CDKN2A G500 allele is more frequent in GBM patients with no defined telomere maintenance mechanism tumors and is associated with poorer survival

Prognostic markers for glioblastoma multiforme (GBM) are important for patient management. Recent advances have identified prognostic markers for GBMs that use telomerase or the alternative lengthening of telomeres (ALT) mechanism for telomere maintenance. Approximately 40% of GBMs have no defined telomere maintenance mechanism (NDTMM), with a mixed survival for affected individuals. This study examined genetic variants in the cyclin-dependent kinase inhibitor 2A (CDKN2A) gene that encodes the p16^INK4a and p14^ARF tumor suppressors, and the isocitrate dehydrogenase 1 (IDH1) gene as potential markers of survival for 40 individuals with NDTMM GBMs (telomerase negative and ALT negative by standard assays), 50 individuals with telomerase, and 17 individuals with ALT positive tumors. The analysis of CDKN2A showed NDTMM GBMs had an increased minor allele frequency for the C500G (rs11515) polymorphism compared to those with telomerase and ALT positive GBMs (p = 0.002). Patients with the G500 allele had reduced survival that was independent of age, extent of surgery, and treatment. In the NDTMM group G500 allele carriers had increased loss of CDKN2A gene dosage compared to C500 homozygotes. An analysis of IDH1 mutations showed the R132H mutation was associated with ALT positive tumors, and was largely absent in NDTMM and telomerase positive tumors. In the ALT positive tumors cohort, IDH1 mutations were associated with a younger age for the affected individual. In conclusion, the G500 CDKN2A allele was associated with NDTMM GBMs from older individuals with poorer survival. Mutations in IDH1 were not associated with NDTMM GBMs, and instead were a marker for ALT positive tumors in younger individuals.

Potential clinical role of telomere length in human glioblastoma

Glioblastoma Multiforme (GBM) is the most common and lethal of human primary central nervous system (CNS) tumors. Due to the tumour's intrinsic clinical and molecular heterogeneity, choice of initial treatment, prediction of survival, stratification of patients, prediction and monitoring of response to therapy, represent some of the greatest challenges in the management of GBM patients. Patients, despite optimal surgery, radiation and chemotherapy, still have a median survival of 14-16 months. A reason for this dismal prognosis is because of the relative inaccuracy of current prognostic markers, so far based on clinical or pathological variables. Molecular markers that effectively predict response to therapy and survival outcomes are limited. Consequently, there is a strong need to develop novel and independent markers of prognosis. Ideal biomarkers for solid tumors would serve one or more important functions. Telomeres, guanine-rich tandem DNA repeats of the chromosomal end, provide chromosomal stability, regulates important cellular processes, and seem to be implicated in human carcinogenesis. Recently, telomeres have been shown either to be associated with clinical markers of disease progression or to be independent markers of cancer prognosis in solid tumours, including GBM. Nevertheless, a corresponding comprehensive discussion of these promising developments in brain tumours has not yet been available in the literature. Therefore, here we reviewed studies focused on the assessment of telomeric length in brain tumours with the aim to emphasized those findings indicating a potential clinical role of telomeres in GBM. With the aim to enhance the awareness of the potential clinical role of telomeres' length information in GBM, using a southern blot analysis, telomeric length in excised tumour samples was analyzed. Moreover, an attempt to correlated telomere length with patients' overall survival, was also performed. The findings here reviewed shows some contradictory results, due to different tissues used as controls, but mainly to cellular and molecular heterogeneity in GBMs that drive molecular mechanisms controlling telomere length, included telomerase and Alternative Lengthening of Telomeres (ALT), through multiple mechanisms. However, overall these studies, including our own, are consistent with the hypothesis that GBMs' telomeres were always shorter when compared with Normal Brain Tissue (NBT), and together with higher telomerase activity seem to be associated with malignancy and poor outcome; while tumours with ALT phenotype have longer telomeres, "less malignant" behaviour and better prognosis. We conclude that, although not entirely consistent in the type of telomere alteration, i.e., attrition vs. elongation, and unclear on the underlying mechanisms, multiple studies in brain tumours have shown that telomere dysfunctions are associated with parameters of clinical outcome in patients with GBMs and therefore will be part of novel risk assessment and prognostic modalities for patients with these still dismal disease.

Genetic aberrations leading to MAPK pathway activation mediate oncogene-induced senescence in sporadic pilocytic astrocytomas

PURPOSE

Oncogenic BRAF/Ras or NF1 loss can potentially trigger oncogene-induced senescence (OIS) through activation of the mitogen-activated protein kinase (MAPK) pathway. Somatic genetic abnormalities affecting this pathway occur in the majority of pilocytic astrocytomas (PA), the most prevalent brain neoplasm in children. We investigated whether OIS is induced in PA.

EXPERIMENTAL DESIGN

We tested expression of established senescence markers in three independent cohorts of sporadic PA. We also assessed for OIS in vitro, using forced expression of wild-type and V600E-mutant BRAF in two astrocytic cell lines: human telomerase reverse transcriptase (hTERT)-immortalized astrocytes and fetal astrocytes.

RESULTS

Our results indicate that PAs are senescent as evidenced by marked senescence-associated acidic β-galactosidase activity, low KI-67 index, and induction of p16(INK4a) but not p53 in the majority of 52 PA samples (46 of 52; 88.5%). Overexpression of a number of senescence-associated genes [CDKN2A (p16), CDKN1A (p21), CEBPB, GADD45A, and IGFBP7] was shown at the mRNA level in two independent PA tumor series. In vitro, sustained activation of wild-type or mutant BRAF induced OIS in both astrocytic cell lines. Loss of p16(INK4a) in immortalized astrocytes abrogated OIS, indicative of the role of this pathway in mediating this phenomenon in astrocytes. OIS is a mechanism of tumor suppression that restricts the progression of benign tumors. We show that it is triggered in PAs through p16(INK4a) pathway induction following aberrant MAPK activation.

CONCLUSIONS

OIS may account for the slow growth pattern in PA, the lack of progression to higher-grade astrocytomas, and the high overall survival of affected patients.

BRAF-KIAA1549 fusion predicts better clinical outcome in pediatric low-grade astrocytoma

PURPOSE

Recent studies have revealed that the majority of pediatric low-grade astrocytomas (PLGA) harbor the BRAF-KIAA1549 (B-K) fusion gene resulting in constitutive activation of the RAS/MAPK pathway. However, the clinical significance of this genetic alteration is yet to be determined. We aimed to test the prognostic role of the B-K fusion in progression of incompletely resected PLGA.

EXPERIMENTAL DESIGN

We retrospectively identified 70 consecutive patients with incompletely resected "clinically relevant" PLGA. We added 76 tumors diagnosed at our institution between 1985 and 2010 as controls. We examined BRAF alterations by reverse transcriptase PCR, FISH, and single-nucleotide polymorphism array analysis and correlated that with progression-free survival (PFS).

RESULTS

Overall, 60% of tumors were B-K fusion positive. All patients with B-K fused PLGA are still alive. Five-year PFS was 61% ± 8% and 18% ± 8% for fusion positive and negative patients, respectively (P = 0.0004). B-K fusion resulted in similarly significant favorable PFS for patients who received chemotherapy. Multivariate analysis revealed that B-K fusion was the most significant favorable prognostic factor in incompletely resected PLGA and was independent of location, pathology, and age. In vitro, BRAF overexpression resulted in growth arrest associated with DNA damage (γH2AX expression). Five-year PFS was 68% ± 15% and 0% for patients with B-K fused and γH2AX-expressing PLGA versus negative tumors (P = 0.001).

CONCLUSION

These data suggest that B-K fusion confers a less aggressive clinical phenotype on PLGA and may explain their tendency to growth arrest. Combined analysis of B-K fusion and γH2AX expression can determine prognosis and may be a powerful tool to tailor therapy for these patients.

Spontaneous regression of multicentric pilocytic astrocytoma with CSF dissemination in an adult

We present a case of spontaneous regression of multicentric pilocytic astrocytoma with cerebrospinal fluid (CSF) dissemination without neurofibromatosis type 1 (NF1) in an adult, the first such case reported. Magnetic resonance imaging (MRI) showed multiple low signal intensity lesions on T1-weighted images and high signal intensity areas on T2-weighted images in the bilateral thalamus, basal ganglia and midbrain. Contrast-enhanced MRI revealed that small, enhanced lesions were seen in the basal ganglia and the pineal region. Neuroendoscopic biopsy and third ventriculostomy were performed. Intraoperative findings demonstrated CSF dissemination. Histologically, the specimens showed pilocytic astrocytoma. Serial MRIs showed regression of the tumor without any additional treatment. The clinical features of spontaneous regression of pilocytic astrocytoma are discussed.

Pilocytic astrocytomas have telomere-associated promyelocytic leukemia bodies without alternatively lengthened telomeres

Telomere maintenance by either telomerase activity or the recombination-mediated alternative lengthening of telomeres (ALT) mechanism is a hallmark of cancer. Tumors that use ALT as their telomere maintenance mechanism are characterized by long telomeres of great heterogeneity in length and by specific nuclear structures of co-localized promyelocytic leukemia protein and telomere DNA, called ALT-associated promyelocytic leukemia bodies (APBs). Recent advances have revealed a direct role for APBs in telomere recombination in ALT-positive cells. In this study, we investigated the possibility that APBs could occur before the long 'alternatively' lengthened telomeres arise, particularly in low-grade tumors. We measured APBs, telomere length, and telomerase activity in 64 astrocytomas inclusive of grade 1-4 tumors. Almost all grade 1-3 tumors (93%) were APB-positive using published criteria. Grade 2-3 APB-positive tumors also had long telomeres and were confirmed as ALT positive. However, grade 1 tumors lacked long telomeres and were therefore classified as ALT negative, but positive for telomere-associated promyelocytic leukemia bodies (TPB). This is the first report of a TPB-positive but ALT-negative tumor, and suggests that low-grade tumors have the foundation for recombinational telomere repair, as in ALT. Further work is warranted to characterize the TPB-positive phenotype in other early malignancies, as well as to determine whether TPBs predispose to telomere maintenance by ALT.

Telomerase inhibition as a novel therapy for pediatric ependymoma

Ependymomas are the third most common pediatric brain tumor with an overall survival of approximately 50%. Recently, we showed that telomerase [human telomerase reverse transcriptase (hTERT)] expression is a predictor of poor outcome in pediatric ependymoma. Thus, we hypothesized that ependymomas with functional telomerase may behave more aggressively and that these patients may benefit from anti-telomerase therapy. To address our hypothesis, we investigated the effect of telomerase inhibition on primary ependymoma cells harvested at the time of surgery, as no animal models or established cell lines are readily available for this tumor. The cells were characterized for glial fibrillary acidic protein (GFAP) and hTERT expression, initial telomere length and telomerase activity. They were then subjected to telomerase inhibition (MST-312, 1 microM) and tested for effects on cell viability (MTT assay), proliferation (MIB-1), apoptosis (cleaved caspase 3) and DNA damage (gammaH2AX). After 72 h of telomerase inhibition, primary ependymoma cells showed a significant decrease in cell number (P < 0.001), accompanied by increased DNA damage (gammaH2AX expression) (P < 0.01) and decreased proliferative index (MIB-1) (P < 0.01). Half showed an increase in apoptosis (cleaved caspase 3). These data suggest that telomerase inhibition may be an effective adjuvant therapy in pediatric ependymoma, potentially inducing tumor growth arrest in the short term, independent of telomere shortening.

Pediatric low-grade gliomas

Pediatric low-grade gliomas encompass a heterogeneous set of tumors of different histologies. Cerebellar pilocytic astrocytomas occur most frequently followed by supratentorial diffuse fibrillary astrocytomas. Recent research has implicated activation of the RAS/RAF/MEK pathway in tumorigenesis of these tumors. Surgery is the mainstay of therapy. Overall survival rates for patients whose tumors are completely resected are 90% or greater, 10 years from diagnosis. Conversely, most optic pathway/hypothalamic, deep midline, and brain stem gliomas have minimal potential for resection; these tumors can be difficult to treat and deserve special attention. Combination chemotherapy is currently recommended as front-line adjuvant treatment for progressive or recurrent tumors. Second-line radiotherapy can also improve overall survival but is associated with more frequent and significant neurocognitive, endocrine, and other long-term toxicities.

Impact of morphology, MIB-1, p53 and MGMT on outcome in pilocytic astrocytomas

Pilocytic astrocytoma (PA) is the most common glioma in the pediatric population. PAs can exhibit variable behavior that does not always correlate with location, yet at present there is no way to predict which tumors will be more aggressive. To address this problem, an institutional cohort of 147 PAs (118 with outcome data) from both cerebellar and noncerebellar locations (spine, diencephalon, midbrain, brainstem and cortex) was utilized. Parameters included quantification of characteristic morphologic variables as well as genes previously shown to be of relevance in high-grade gliomas, including MIB-1, p53 and MGMT. In this cohort, the classic biphasic appearance was most common in cerebellar tumors, whereas noncerebellar tumors were predominantly microcystic. Associations with outcome suggest that the presence of degenerative atypia may be a favorable factor in PAs. Oligodendroglial morphology and the absence of leptomeningeal invasion are adverse histologic factors, but only in cerebellar tumors. Conversely, MIB-1 proliferation index and p53 and MGMT expression do not correlate with outcome. Morphologic biomarkers thus do exist for PAs, but the utility of each biomarker varies according to location. These results suggest that PAs differ fundamentally according to location; therefore, biological behavior may not simply depend on extent of resection.

Survival and functional outcome of childhood spinal cord low-grade gliomas. Clinical article

OBJECT

Intramedullary spinal cord low-grade gliomas (LGGs) are rare CNS neoplasms in pediatric patients, and there is little information on therapy for and outcome of these tumors in this population. Furthermore, most patient series combine adult and pediatric patients or high- and low-grade tumors, resulting in controversial data regarding optimal treatment of these children. To clarify these issues, the authors performed a regional population-based study of spinal cord LGGs in pediatric patients.

METHODS

All pediatric patients with LGGs treated during the MR imaging era (1985-2007) were identified in the comprehensive database of the Hospital for Sick Children in Toronto. Data on demographics, pathology, treatment details, and outcomes were collected.

RESULTS

Spinal cord LGGs in pediatric patients constituted 29 (4.6%) of 635 LGGs. Epidemiological and clinical data in this cohort were different than in patients with other spinal tumors and strikingly similar to data from pediatric patients with intracranial LGGs. The authors observed an age peak at 2 years and a male predominance in patients with these tumors. Histological testing revealed a Grade I astrocytoma in 86% of tumors. Although 5-year progression-free survival for the entire group was 48 +/- 9%, all patients were alive at a median follow-up of 8.2 years. Five-year progression-free survival was 88 +/- 13% for patients undergoing gross-total resection and 34 +/- 11% for those undergoing all other therapies, respectively (p = 0.02). Chemotherapy and radiation therapy showed similar efficacy, achieving sustained tumor control in most patients. However, this excellent survival rate was associated with an 83% rate of significant neurological and orthopedic sequelae.

CONCLUSIONS

This study provides basic data on the incidence, clinical course, and outcome of spinal cord LGGs in pediatric patients. The similarities between spinal and intracranial LGGs in pediatric patients showing excellent survival but high morbidity suggest that a less aggressive approach may be the preferable treatment option for these patients.

Pediatric ependymoma: biological perspectives

Pediatric ependymomas are enigmatic tumors that continue to present a clinical management challenge despite advances in neurosurgery, neuroimaging techniques, and radiation therapy. Difficulty in predicting tumor behavior from clinical and histological factors has shifted the focus to the molecular and cellular biology of ependymoma in order to identify new correlates of disease outcome and novel therapeutic targets. This article reviews our current understanding of pediatric ependymoma biology and includes a meta-analysis of all comparative genomic hybridization (CGH) studies done on primary ependymomas to date, examining more than 300 tumors. From this meta-analysis and a review of the literature, we show that ependymomas in children exhibit a different genomic profile to those in adults and reinforce the evidence that ependymomas from different locations within the central nervous system (CNS) are distinguishable at a genomic level. Potential biological markers of prognosis in pediatric ependymoma are assessed and the ependymoma cancer stem cell hypothesis is highlighted with respect to tumor resistance and recurrence. We also discuss the shifting paradigm for treatment modalities in ependymoma that target molecular alterations in tumor-initiating cell populations.