Morphological and molecular features of astroblastoma, including BRAFV600E mutations, suggest an ontological relationship to other cortical-based gliomas of children and young adults

Awake resection of recurrent astroblastoma with intraoperative 5-ALA-induced fluorescence: illustrative case

BACKGROUND

Astroblastoma is a rare neoplasm characterized as a circumscribed glial neoplasm most often arising in the frontoparietal cerebral hemispheres in older children.

OBSERVATIONS

We report an intriguing case of an astroblastoma recurrence 21 years after gross-total resection and radiation. A 32-year-old right-handed female presented to the emergency department for a generalized tonic-clonic seizure. She had a history of bipolar disorder, intractable migraines, and prior seizures linked to an astroblastoma previously resected three times. Magnetic resonance imaging on the current visit showed growth of the recurrent lesion to a 3.8-cm maximal diameter. Left-sided awake craniotomy was performed to remove the tumor while using speech mapping and 5-aminolevulinic acid (5-ALA). Targeted next-generation sequencing of the tumor revealed in-frame MN1::BEND2 fusion transcripts.

LESSONS

We found that 5-ALA can be used in astroblastoma patients to assist in gross-total resection, which is important for long-term survival. Our astroblastoma case demonstrated classic astroblastoma morphology, with typical perivascular astroblastic rosettes, and was brightly fluorescent after 5-ALA administration.

Successes and challenges in modeling heterogeneous BRAFV600E mutated central nervous system neoplasms

Central nervous system (CNS) neoplasms are difficult to treat due to their sensitive location. Over the past two decades, the availability of patient tumor materials facilitated large scale genomic and epigenomic profiling studies, which have resulted in detailed insights into the molecular underpinnings of CNS tumorigenesis. Based on results from these studies, CNS tumors have high molecular and cellular intra-tumoral and inter-tumoral heterogeneity. CNS cancer models have yet to reflect the broad diversity of CNS tumors and patients and the lack of such faithful cancer models represents a major bottleneck to urgently needed innovations in CNS cancer treatment. Pediatric cancer model development is lagging behind adult tumor model development, which is why we focus this review on CNS tumors mutated for BRAFV600E which are more prevalent in the pediatric patient population. BRAFV600E-mutated CNS tumors exhibit high inter-tumoral heterogeneity, encompassing clinically and histopathological diverse tumor types. Moreover, BRAFV600E is the second most common alteration in pediatric low-grade CNS tumors, and low-grade tumors are notoriously difficult to recapitulate in vitro and in vivo. Although the mutation predominates in low-grade CNS tumors, when combined with other mutations, most commonly CDKN2A deletion, BRAFV600E-mutated CNS tumors are prone to develop high-grade features, and therefore BRAFV600E-mutated CNS are a paradigm for tumor progression. Here, we describe existing in vitro and in vivo models of BRAFV600E-mutated CNS tumors, including patient-derived cell lines, patient-derived xenografts, syngeneic models, and genetically engineered mouse models, along with their advantages and shortcomings. We discuss which research gaps each model might be best suited to answer, and identify those areas in model development that need to be strengthened further. We highlight areas of potential research focus that will lead to the heightened predictive capacity of preclinical studies, allow for appropriate validation, and ultimately improve the success of "bench to bedside" translational research.

Radiology-Pathology and Surgical Correlation in Astroblastoma

Astroblastoma is a rare astrocytic glial neoplasm that affects mainly young girls, peaking between 10 and 30 years of age, with low- and high-grade manifestations. Imaging characteristics are well-described, but histopathologic and, more recently, molecular analysis is fundamental to establish the diagnosis, now based on MN1 alterations. We describe a case with typical imaging and histologic features of an MN1-altered astroblastoma.

Early ependymal tumor with MN1-BEND2 fusion: a mostly cerebral tumor of female children with a good prognosis that is distinct from classical astroblastoma

PURPOSE

Review of the clinicopathologic and genetic features of early ependymal tumor with MN1-BEND2 fusion (EET MN1-BEND2), classical astroblastomas, and recently described related pediatric CNS tumors. I also briefly review general mechanisms of gene expression silencing by DNA methylation and chromatin remodeling, and genomic DNA methylation profiling as a powerful new tool for CNS tumor classification.

METHODS

Literature review and illustration of tumor histopathologic features and prenatal gene expression timelines.

RESULTS

Astroblastoma, originally descried by Bailey and Cushing in 1926, has been an enigmatic tumor. Whether they are of ependymal or astrocytic derivation was argued for decades. Recent genetic evidence supports existence of both ependymal and astrocytic astroblastoma-like tumors. Studies have shown that tumors exhibiting astroblastoma-like histology can be classified into discrete entities based on their genomic DNA methylation profiles, gene expression, and in some cases, the presence of unique gene fusions. One such tumor, EET MN1-BEND2 occurs mostly in female children, and has an overall very good prognosis with surgical management. It contains a gene fusion comprised of portions of the MN1 gene at chromosomal location 22q12.1 and the BEND2 gene at Xp22.13. Other emerging pediatric CNS tumor entities demonstrating ependymal or astroblastoma-like histological features also harbor gene fusions involving chromosome X, 11q22 and 22q12 breakpoint regions.

CONCLUSIONS

Genomic DNA profiling has facilitated discovery of several new CNS tumor entities, however, traditional methods, such as immunohistochemistry, DNA or RNA sequencing, and cytogenetic studies, including fluorescence in situ hybridization, remain necessary for their accurate biological classification and diagnosis.

Implications of BRAF V600E mutation in gliomas: Molecular considerations, prognostic value and treatment evolution

Gliomas are molecularly heterogeneous brain tumors responsible for the most years of life lost by any cancer. High-grade gliomas have a poor prognosis and despite multimodal treatment including surgery, radiotherapy, and chemotherapy, exhibit a high recurrence rate. There is a need for new therapeutic approaches based on precision medicine informed by biomarker assessment and BRAF, a key regulator of MAPK signaling pathway, influencing cell differentiation, proliferation, migration and pro-tumorigenic activity, is emerging as a promising molecular target. V600E, is the most frequent BRAF alteration in gliomas, especially in pediatric low-grade astrocytomas, pleomorphic xanthoastrocytoma, papillary craniopharyngioma, epithelioid glioblastoma and ganglioglioma. The possible application of BRAF-targeted therapy in gliomas is continuously growing and there is preliminary evidence of prolonged disease control obtained by BRAF inhibitors in tumors harboring BRAF V600E mutation. The possibility of introducing targeted therapies into the treatment algorithm represents a paradigm shift for patients with BRAF V600E mutant recurrent high-grade and low-grade glioma and BRAF routine testing should be considered in clinical practice. The focus of this review is to summarize the molecular landscape of BRAF across glioma subtypes and the novel therapeutic strategies for BRAF V600E mutated tumors.

The evolution of pleomorphic xanthoastrocytoma: from genesis to molecular alterations and mimics

Pleomorphic xanthoastrocytomas (PXAs) are rare tumors accounting for less than 1% of astrocytomas. They commonly occur in young patients and have relatively favorable prognosis. However, they are well known to have heterogenous morphology and biological behavior with the potential to recur and disseminate throughout the central nervous system, especially their anaplastic counterparts. Recent advances in the molecular characterization have discovered BRAFp.V600E mutations in conjunction with CDKN2A/B deletions and TERTp mutations to be the most frequent alterations in PXAs. These tumors can present a diagnostic challenge as they share overlapping histopathological, genomic as well as methylation profile with various other tumor types, particularly epithelioid glioblastomas (eGBs). This review provides the spectrum of evolution of PXAs from their genesis to recent molecular insights and attempts to review pathogenesis and relationship to other tumors that they mimic especially eGB. It is postulated based on evidence from literature that PXA and eGB are possibly related and not distinct entities, being two ends of a continuous spectrum of malignant progression (grade 2-grade 4) with anaplastic PXA (grade 3) lying in between. Future WHO classifications will have to possibly redefine these tumors using more confirmatory data from larger studies.

Thirteen-year long-term follow-up in a rare case of anaplastic astroblastoma: What makes the difference?

Background:

Astroblastomas are uncommon neuroepithelial tumors of the central nervous system with a distinct, yet, controversial radiological, histological, and molecular profile. Debatable differences between low- and high-grade astroblastoma have been reported in the medical literature; indeed, despite the increasing relevance of molecular genetic profiling in the realm of astroblastoma, its application is still in its early stages. As a result, the diagnostic criteria for astroblastoma remain undecided with yet no real consensus on the most ideal management.

Case Description:

This report describes a case of astroblastoma diagnosed 13 years ago in a young woman who despite six episodes of recurrence, transformation, and progression was able to retain a perfomace status of 0 by World Health Organization standard, throughout.

Conclusion:

This report discusses the clinical, radiological, histological features, and management of this rare tumor with an extraordinarily long survival, with an aim to strengthen the literature on management options. To the best of our knowledge, this is the longest surviving case of anaplastic astroblastoma reported in the available medical literature.

Astroblastomas exhibit radial glia stem cell lineages and differential expression of imprinted and X-inactivation escape genes

Astroblastomas (ABs) are rare brain tumors of unknown origin. We performed an integrative genetic and epigenetic analysis of AB-like tumors. Here, we show that tumors traceable to neural stem/progenitor cells (radial glia) that emerge during early to later brain development occur in children and young adults, respectively. Tumors with MN1-BEND2 fusion appear to present exclusively in females and exhibit overexpression of genes expressed prior to 25 post-conception weeks (pcw), including genes enriched in early ventricular zone radial glia and ependymal tumors. Other, histologically classic ABs overexpress or harbor mutations of mitogen-activated protein kinase pathway genes, outer and truncated radial glia genes, and genes expressed after 25 pcw, including neuronal and astrocyte markers. Findings support that AB-like tumors arise in the context of epigenetic and genetic changes in neural progenitors. Selective gene fusion, variable imprinting and/or chromosome X-inactivation escape resulting in biallelic overexpression may contribute to female predominance of AB molecular subtypes.

Recurrent HGNET-MN1 altered (astroblastoma MN1-altered) of the foramen magnum: Case report and molecular classification

Background:

Astroblastoma is a rare primary brain tumor of unclear origin, often occurring in young patients less than 30-years-old. It typically arises supratentorially and is diagnosed based on histological features including vascular hyalinization and perivascular pseudorosettes. Recent molecular characterization of primary CNS high-grade neuroepithelial tumors with meningioma I alteration (HGNET-MN1) found that HGNET-MN1 and tumors with morphological signatures of astroblastoma clustered together. Further analysis revealed such astroblastomas have MN1 alteration and the 2021 WHO classification of tumors of the CNS now recognizes astroblastoma MN1-altered as a new entity.

Case Description:

Here, we present the case of a 36-year-old right-handed woman with recurrent low-grade astroblastoma in the cervicomedullary junction. The patient presented with worsening motor and sensory deficits of her upper extremities, pain, ataxia, visual disturbance, and nausea. Due to extensive recurrence and neurological symptoms, the patient underwent reoperation.

Conclusion:

We review a rare case of recurrent astroblastoma in the foramen magnum in light of new relevant literature about tumor biology and prognostic significance of the new classification of astroblastoma MN1-altered.

Clinicoradiological and histopathological characteristics and treatment outcomes of cerebral astroblastoma in children: a single-institution experience

OBJECTIVE

Astroblastoma (AB) is a rare glial tumor. The optimal treatment and prognosis of this tumor remain unclear. The authors retrospectively analyzed the clinical characteristics, neuroimaging findings, histopathological results, and treatment outcomes of 7 patients with AB.

METHODS

The study comprised 7 patients with pathologically proven AB who were surgically treated at Samsung Medical Center from November 1994 to January 2019. Clinicoradiological, histopathological, and surgical records were reviewed.

RESULTS

The patients included 5 girls (71.4%) and 2 boys (28.6%), with a median age of 13 years. All patients showed contrast enhancement on preoperative MRI: 5 ABs (71.4%) showed a concomitant solid and cystic appearance, and 2 (28.6%) demonstrated a solid appearance. ABs in 6 patients (85.7%) showed a well-circumscribed, characteristic "bubbly" appearance on T2-weighted MRI. Gross-total resection (GTR) was achieved in all cases (100%). Six patients (85.7%) were diagnosed with high-grade AB and 1 (14.3%) with low-grade AB. Six (85.7%) of the 7 patients received adjuvant treatment after resection, including 5 (83.3%) with AB who received chemotherapy and radiotherapy and 1 (16.7%) who received proton therapy alone. The median clinical follow-up duration was 96 months (range 48-189 months). Two patients experienced recurrence, and all patients in this series were alive at the last follow-up.

CONCLUSIONS

In this study, the clinicoradiological and histopathological features of AB were described. Based on the authors' limited experience with 7 cases, resection with the goal of GTR is currently the mainstream treatment for AB, and adjuvant radiation treatment should be considered after surgery.

Gene expression based profiling of pleomorphic xanthoastrocytoma highlights two prognostic subgroups

BACKGROUND

Pleomorphic xanthoastrocytomas (PXAs) are rare, accounting for less than 1% of astrocytomas, and commonly occur in young patients. The majority are WHO grade II. A fraction of tumors that present or recur with malignant change are classified as anaplastic (APXA, grade III). Limited data are available on their molecular characteristics.

METHODOLOGY

Genome-wide expression profiling of 14 PXA and 6 APXAs was performed by microarray. Among differentially expressed genes (DEGs), Cyclin-Dependent Kinase 14 (CDK14) and Mitochondrial Fission Process 1 (MTFP1) were validated by qRT PCR.

RESULT

Unsupervised hierarchical clustering revealed two distinct molecular clusters (Cluster 1: 10 PXA, 3 APXA and Cluster 2: 4 PXA, 3 APXA) with grade II and III tumors distributed in both highlighting molecular heterogeneity within the same grade. There was an insignificant difference in age, sex, immunohistochemical profile, frequency of BRAF mutation, or CDKN2A deletion among the two clusters. Significantly, worse progression-free survival was observed in cluster 2 (P=0.003). mRNA profiling-based prediction of recurrence was superior to and independent of histological grade, BRAF mutation, or CDKN2A deletion status. A total of 10 upregulated and 418 downregulated genes were identified between the PXA clusters. qRT-PCR validation of CDK14 (upregulated in cluster 2) and MTFP1 (upregulated in cluster 1) showed strong concordance with expression array data.

CONCLUSION

This is the first comprehensive study highlighting distinct molecular subgroups of PXA. The differentially expressed genes between two clusters may potentially be used for developing histology independent classification schemes, prognostication and may serve as prospective therapeutic targets for PXA patients.

Adolescent and young adult brain tumors: current topics and review

The management of brain tumors developed in adolescents and young adults (AYAs) is challenging because of their histological heterogeneity and low incidence. The brain tumor and its treatment interventions can negatively affect neurological, neurocognitive, and endocrinological function, and dramatically affect the circumstances of AYA patients progressing to further education, employment, and marriage. Specific support is thus necessary to maintain the quality of life (QOL) of AYA brain tumor patients. AYA patients and survivors require active intervention and support for returning to school or work, progressing to further education, finding employment, and preserving fertility. Recent cancer genome profiling revealed that AYA gliomas include pediatric- and adult-type genetic alteration. Insights into the biology underlying the distribution of tumors in AYAs may influence the development of prospective trials. A more individualized view of brain tumors may influence stratification of patients' in future clinical studies as well as selection for molecular targeted therapy. Here I review strategies for achieving a better outcome to decrease late effects and improve QOL.

Cerebral astroblastoma with oligodendroglial-like cells: A case report

RATIONALE

Astroblastoma is a rare tumor of the central nervous system with uncertain biological behavior and origin. Its histopathological features have been well established, while, to our knowledge, astroblastoma with oligodendroglial-like cells have not been reported.

PATIENT CONCERNS

A 15-year-old girl presented with nausea, vomiting, headache, and visual disturbance.

DIAGNOSIS

Magnetic resonance imaging revealed a large neoplasm in the left temporal. Histologically, the tumor showed solid and pseudopapillary structure. Immunohistochemical staining showed that the tumor cells were positive for glial fibrillary acidic protein and vimentin. The oligodendroglial-like cells were positive for glial fibrillary acidic protein, vimentin, and oligodendrocyte transcription factor 2. The antigen KI67 labeling index was about 4%. Sequencing for isocitrate dehydrogenase (IDH) 1 codon 132 and IDH2 codon 172 gene mutations showed negative results. Furthermore, fluorescent analysis revealed neither 1p nor 19q deletion in the lesion. Based on these findings, the girl was finally diagnosed as astroblastoma.

INTERVENTIONS

A craniotomy with total excision of the tumor was performed.

OUTCOMES

The follow-up time was 1 year, no evidence of disease recurrence was found in magnetic resonance imaging.

LESSONS

Cerebral astroblastoma with oligodendroglial-like cells is a clinically rare tumor of central nervous system. Clear distinction and diagnosis are critical.

Spinal cord astroblastoma with EWSR1-BEND2 fusion classified as HGNET-MN1 by methylation classification: a case report

The most recurrent fusion of central nervous system high-grade neuroepithelial tumor with MN1 alteration (HGNET-MN1) is MN1 rearrangement. Here, we report the case of a 36-year-old man with spinal cord astroblastoma showing Ewing Sarcoma breakpoint region 1/EWS RNA-binding protein 1 (EWSR1)-BEN domain-containing 2 (BEND2) fusion. The patient presented with back pain, gait disturbance and dysesthesia in the lower extremities and trunk. Magnetic resonance imaging showed an intramedullary tumor at the T3-5 level, displaying homogeneous gadolinium enhancement. Partial tumor removal was performed with laminectomy. Histological examinations demonstrated solid growth of epithelioid tumor cells showing high cellularity, a pseudopapillary structure, intervening hyalinized fibrous stroma, and some mitoses. Astroblastoma was diagnosed, classified as HGNET-MN1 by the German Cancer Research Center methylation classifier. MN1 alteration was not detected by fluorescence in situ hybridization (FISH), but EWSR1-BEND2 fusion was detected by FISH and RNA sequencing. Previously, a child with EWSR1-BEND2 fusion-positive spinal astroblastoma classified as HGNET-MN1 was reported. In conjunction with that, the present case provides evidence that EWSR1-BEND2 fusion is identified in the entity of HGNET-MN1. Taken together, the BEND2 alteration rather than MN1 may determine the biology of a subset of the central nervous system HGNET-MN1 subclass.

Cerebral Astroblastoma: A Rare Tumor

Astroblastoma is a rare neuroepithelial tumor of the central nervous system, which accounts for only 0.45-2.8% of all neuroglial tumors. These tumors have distinct radiological, histopathological, immunohistochemical, and molecular features. We describe a case of astroblastoma of the left temporal lobe in a 38-year-old female, who presented with complaints of headache and occasional episodes of vomiting.

A Rare Case of a High-Grade Astroblastoma with 5-Year Follow-up

Astroblastoma is a very rare glial tumor derived from astroblasts. It has been controversial in terms of its features and diagnosis. The objective of this report is to present the findings of the high-grade astroblastoma with a good prognosis in a 21-year-old female who presented to us with diplopia and headache. While imaging led to the foremost differentials of pleomorphic xanthoastrocytoma and Ganglioglioma which are low-grade neoplasms, the final diagnosis was established on microscopy and immunohistochemistry after excision. Treatment protocol included surgery with postoperative radiotherapy and chemotherapy. Due to controversial and limited literature, this tumor poses difficulties in diagnosis and management. This is a rare, successfully managed case of astroblastoma with a positive outcome 5 years after the diagnosis was established. In this case report, we review the steps of diagnosis, the differentials, the pathological and histological features, and the management of this rare entity.

Central nervous system neuroepithelial tumors with MN1-alteration: an individual patient data meta-analysis of 73 cases

MN1 alteration characterizes a recently described group of neuroepithelial tumors with varied morphological features. In cIMPACT-NOW update 6, only those with astroblastoma morphology has been accepted as a newly recognized tumor type, whereas the rest of morphological variants are considered lesions sub-judice. We perform an individual patient data meta-analysis of MN1-altered neuroepithelial tumors comprising a total of 73 cases, in order to study the survival data and predictive markers for better diagnosis and management of this rare molecular entity. The 5- and 10-year progression-free survival are 38% and 0%, whereas the 5- and 10-year overall survival are 89% and 55%, respectively. Among all the morphological variants of MN1-altered tumor, astroblastoma morphology is significantly associated with an improved overall survival, emphasizing the importance of providing an integrated histologic and molecular diagnosis. Histological grading within the molecularly-defined MN1-altered astroblastoma remains controversial. In tumors with astroblastoma morphology, the odds of MN1-altered status among patients less than 15-year-old is 10.5 times that of those 15-year-old and older, and female of 9.4 times that of the male gender. Gross tumor resection appears as main treatment modality for better disease control based on observational data.

Targeted fusion analysis can aid in the classification and treatment of pediatric glioma, ependymoma, and glioneuronal tumors

BACKGROUND

The use of next-generation sequencing for fusion identification is being increasingly applied and aids our understanding of tumor biology. Some fusions are responsive to approved targeted agents, while others have future potential for therapeutic targeting. Although some pediatric central nervous system tumors may be cured with surgery alone, many require adjuvant therapy associated with acute and long-term toxicities. Identification of targetable fusions can shift the treatment paradigm toward earlier integration of molecularly targeted agents.

METHODS

Patients diagnosed with glial, glioneuronal, and ependymal tumors between 2002 and 2019 were retrospectively reviewed for fusion testing. Testing was done primarily using the ArcherDx FusionPlex Solid Tumor panel, which assesses fusions in 53 genes. In contrast to many previously published series chronicling fusions in pediatric patients, we compared histological features and the tumor classification subtype with the specific fusion identified.

RESULTS

We report 24 cases of glial, glioneuronal, or ependymal tumors from pediatric patients with identified fusions. With the exception of BRAF:KIAA1549 and pilocytic/pilomyxoid astrocytoma morphology, and possibly QKI-MYB and angiocentric glioma, there was not a strong correlation between histological features/tumor subtype and the specific fusion. We report the unusual fusions of PPP1CB-ALK, CIC-LEUTX, FGFR2-KIAA159, and MN1-CXXC5 and detail their morphological features.

CONCLUSIONS

Fusion testing proved to be informative in a high percentage of cases. A large majority of fusion events in pediatric glial, glioneuronal, and ependymal tumors can be identified by relatively small gene panels.

A review of recently described genetic alterations in central nervous system tumors

Advances in molecular profiling of central nervous system tumors have enabled the development of classification schemes with improved diagnostic and prognostic accuracy. As such, the 2016 World Health Organization Classification of Tumors of the Central Nervous System (WHO 2016) introduced a paradigm shift in the diagnosis of brain tumors. For instance, integrated assessment incorporating both histologic features and genetic alterations was introduced into the diagnostic framework of gliomas. IDH1/2 mutation status now represents the most important initial stratifier of diffuse gliomas in adults, although rarer subtypes within the IDH-wildtype category continue to be elucidated. Medulloblastomas and other embryonal neoplasms were also genetically defined and segregated based on molecular subtypes, and 1 molecular subtype of ependymoma was added. In this review, we summarize the rapidly evolving spectrum of recurrent genetic alterations described in central nervous system tumor entities since the publication of the WHO 2016.

Molecular Profiling Reclassifies Adult Astroblastoma into Known and Clinically Distinct Tumor Entities with Frequent Mitogen-Activated Protein Kinase Pathway Alterations

BACKGROUND

Astroblastoma (ABM) is a rare glial brain tumor. Recurrent meningioma 1 (MN1) alterations have been recently identified in most pediatric cases. Adolescent and adult cases, however, remain molecularly poorly defined.

MATERIALS AND METHODS

We performed clinical and molecular characterization of a retrospective cohort of 14 adult and 1 adolescent ABM.

RESULTS

Strikingly, we found that MN1 fusions are a rare event in this age group (1/15). Using methylation profiling and targeted sequencing, most cases were reclassified as either pleomorphic xanthoastrocytomas (PXA)-like or high-grade glioma (HGG)-like. PXA-like ABM show BRAF mutation (6/7 with V600E mutation and 1/7 with G466E mutation) and CD34 expression. Conversely, HGG-like ABM harbored specific alterations of diffuse midline glioma (2/5) or glioblastoma (GBM; 3/5). These latter patients showed an unfavorable clinical course with significantly shorter overall survival (p = .021). Mitogen-activated protein kinase pathway alterations (including FGFR fusion, BRAF and NF1 mutations) were present in 10 of 15 patients and overrepresented in the HGG-like group (3/5) compared with previously reported prevalence of these alterations in GBM and diffuse midline glioma.

CONCLUSION

We suggest that gliomas with astroblastic features include a variety of molecularly sharply defined entities. Adult ABM harboring molecular features of PXA and HGG should be reclassified. Central nervous system high-grade neuroepithelial tumors with MN1 alterations and histology of ABM appear to be uncommon in adults. Astroblastic morphology in adults should thus prompt thorough molecular investigation aiming at a clear histomolecular diagnosis and identifying actionable drug targets, especially in the mitogen-activated protein kinase pathway.

IMPLICATIONS FOR PRACTICE

Astroblastoma (ABM) remains a poorly defined and controversial entity. Although meningioma 1 alterations seem to define a large subset of pediatric cases, adult cases remain molecularly poorly defined. This comprehensive molecular characterization of 1 adolescent and 14 adult ABM revealed that adult ABM histology comprises several molecularly defined entities, which explains clinical diversity and identifies actionable targets. Namely, pleomorphic xanthoastrocytoma-like ABM cases show a favorable prognosis whereas high-grade glioma (glioblastoma and diffuse midline gliome)-like ABM show significantly worse clinical courses. These results call for in-depth molecular analysis of adult gliomas with astroblastic features for diagnostic and therapeutic purposes.

Posterior fossa astroblastoma in a child: a case report and a review of the literature

A 4-year-old girl presented to the hospital with a progressive headache, difficulty walking, and persistent daily vomiting for 3 weeks. Papilledema was observed on fundoscopic examination. A large left cerebellovermian tumor with "bubbly" appearance was discovered. Total removal of the tumor mass was performed, and a diagnosis of low-grade astroblastoma was made. Adjuvant radiotherapy was performed due to the risk of recurrence. The patient is disease-free and has been kept on close follow-up for 6 months. The occurrence of posterior fossa astroblastoma has been rarely reported in the literature. Thus, when a "bubby" appearance enhancing cystic solid tumor is located on the cerebellar hemisphere in a child, an astroblastoma should also be included in the differential diagnosis.

Mutations of the MAPK/TSC/mTOR pathway characterize periventricular glioblastoma with epithelioid SEGA-like morphology-morphological and therapeutic implications

Epithelioid glioblastoma is a recognized glioblastoma variant, recently added to the World Health Organization brain tumor classification, with similar prognosis as the classic variant and B-Raf V600E mutations in 50% of the cases. We identified a new subset of epithelioid glioblastoma with periventricular location and subependymal giant cell astrocytoma (SEGA)-like morphology. Genomic profiling of these tumors revealed driver mutations in NF1, subclonal mutations in TSC1, and a novel driver mutation in MTOR, suggesting upregulation of the MAPK/TSC1/mTOR pathway. Strong mTOR activation was confirmed by immunohistochemistry for the mTOR kinase target 4E-BP1. TSC1 and MTOR mutations have been previously described in low-grade glioma, such as SEGA, and focal cortical dysplasia, respectively, that display large cells with abundant cytoplasm, most likely resulting from the biogenetic signaling of mTOR. Unlike these, the mutations in SEGA-like glioblastoma occurred in the context of other genetic aberrations present in high-grade neoplasms, including in the CDKN2A/B, PIK3R1, PIK3CA and EGFR genes. For one patient with two temporally distinct specimens, the subclonal TSC1 pathogenic mutation was detected only in the specimen showing SEGA-like morphology, indicating requirement for mTOR activation as trigger for specific epithelioid/SEGA-like morphology. As FDA-approved kinase inhibitors are available and target many steps of the MAPK/mTOR pathway, recognition of this new subset of periventricular high-grade gliomas with clear phenotypic-genotypic correlates is essential for prompt biomarker testing and appropriate targeted therapeutic management of these patients.

Extra-axial anaplastic astroblastoma in a 67-year-old woman

Astroblastoma is a rare glial neoplasia of the central nervous system. It is histologically defined by the presence of neoplastic cells with non- or slightly tapering processes arranged around blood vessels (astroblastic rosettes) and conventionally subdivided into well-differentiated and anaplastic. It commonly affects children and young adults, although cases and due to its superficial location in the brain cortex, it can mimic an extra-axial mass on magnetic resonance imagining. Herein, we describe a unique case of pure extra-axial anaplastic astroblastoma in an elderly woman. Awareness that astroblastoma may be also extra-axial and affect older subjects, may be helpful for its identification and differential diagnosis toward more common entities at this site and age of onset, and for appropriate therapeutic management as well.

Oncogenic BRAF Alterations and Their Role in Brain Tumors

Alterations of the v-raf murine sarcoma viral oncogene homolog B (BRAF) have been extensively studied in several tumor entities and are known to drive cell growth in several tumor entities. Effective targeted therapies with mutation-specific small molecule inhibitors have been developed and established for metastasized malignant melanoma. The BRAF V600E mutation and KIAA1549-BRAF fusion are alterations found in several brain tumors and show a distinct prognostic impact in some entities. Besides the diagnostic significance for the classification of central nervous system tumors, these alterations present possible therapy targets that may be exploitable for oncological treatments, as it has been established for malignant melanomas. In this review the different central nervous system tumors harboring BRAF alterations are presented and the diagnostic significance, prognostic role, and therapeutic potential are discussed.

Role of DNA Methylation Profile in Diagnosing Astroblastoma: A Case Report and Literature Review

Astroblastoma is a rare tumor of the central nervous system (CNS) with uncertain clinical behavior. Recently, DNA methylation profiling has been shown to provide a highly robust and reproducible approach for the classification of all CNS tumors across different age groups. By using DNA methylation profiling, a subset of CNS high-grade tumors with astroblastoma-like morphology characterized by the meningioma 1 gene (MN1) rearrangements, has been identified; they were termed “CNS high-grade neuroepithelial tumors with MN1 alteration” (CNS-HGNET-MN1). Here, we describe a case of CNS-HGNET-MN1 diagnosed by DNA methylation profiling, using Illumina Infinium HumanMethylationEPIC BeadChip (EPIC), that offers the opportunity to conduct a brief literature review. The patient presented with an episode of partial seizures involving the right hemisoma. A gross total resection was performed. No other treatment was proposed in light of the histological and molecular findings. After 21 months, the patient is disease-free in good clinical conditions. Also in view of this case, we recommend DNA-methylation profiling as an important tool for diagnosis and more effective patient stratification and management.

Genomic analysis demonstrates that histologically-defined astroblastomas are molecularly heterogeneous and that tumors with MN1 rearrangement exhibit the most favorable prognosis

Astroblastoma (AB) is a rare CNS tumor demonstrating abundant astroblastomatous pseudorosettes. Its molecular features have not been comprehensively studied and its status as a tumor entity is controversial. We analyzed a cohort of 27 histologically-defined ABs using DNA methylation profiling, copy number analysis, FISH and site-directed sequencing. Most cases demonstrated mutually exclusive MN1 rearrangements (n = 10) or BRAF^V600E mutations (n = 7). Two additional cases harbored RELA rearrangements. Other cases lacked these specific genetic alterations (n = 8). By DNA methylation profiling, tumors with MN1 or RELA rearrangement clustered with high-grade neuroepithelial tumor with MN1 alteration (HGNET-MN1) and RELA-fusion ependymoma, respectively. In contrast, BRAF^V600E-mutant tumors grouped with pleomorphic xanthoastrocytoma (PXA). Six additional tumors clustered with either supratentorial pilocytic astrocytoma and ganglioglioma (LGG-PA/GG-ST), normal or reactive cerebrum, or with no defined DNA methylation class. While certain histologic features favored one genetic group over another, no group could be reliably distinguished by histopathology alone. Survival analysis between genetic AB subtypes was limited by sample size, but showed that MN1-rearranged AB tumors were characterized by better overall survival compared to other genetic subtypes, in fact, significantly better than BRAF^V600E-mutant tumors (P = 0.013). Our data confirm that histologically-defined ABs are molecularly heterogeneous and do not represent a single entity. They rather encompass several low- to higher-grade glial tumors including neuroepithelial tumors with MN1 rearrangement, PXA-like tumors, RELA ependymomas, and possibly yet uncharacterized lesions. Genetic subtyping of tumors exhibiting AB histology, particularly determination of MN1 and BRAF^V600E status, is necessary for important prognostic and possible treatment implications.

BRAF V600E-mutated central nervous system tumor with divergent morphological feature - Anaplastic pleomorphic xanthoastrocytoma-like and astroblastoma-like

Mutational analysis of the BRAF gene (BRAF), especially BRAF V600E, is gaining much importance in neuro-oncology practice due to its diagnostic, prognostic and therapeutic implications. This genetic alteration has been described in a wide morphological spectrum of central nervous system tumors. In the present report we describe a BRAF V600E-mutated tumor with divergent morphological appearance comprising of anaplastic pleomorphic xanthoastrocytoma and astroblastoma. Both of these tumor entities are extremely rare and a combined morphology has not been described till now.

Brainstem astroblastoma with MN1 translocation

Astroblastoma is a rare glial neoplasm that occurs mostly in the cerebral hemisphere of children, adolescents and young adults. Although astroblastic perivascular pseudorosettes are unique histopathology of this neoplasm, diagnosis is usually challenging. Recently, it was discovered that the meningioma 1 gene (MN1)-altered pediatric central nervous system high-grade neuroepithelial tumors are actually astroblastomas. This case report presents a rare brainstem astroblastoma, with an unusual immunoprofile: negative for glial fibrillary acidic protein and oligodendrocyte transcription factor 2, but with a robust expression of pancytokeratin and epithelial membrane antigen. The diagnosis was confirmed based on the detection of MN1 rearrangement in a fluorescence in situ hybridization study, in addition to typical histopathology. Here we discuss the diagnostic pitfalls and unclear grading system along with a literature review.

Co-occurrence of astrocytoma and astroblastoma: Case report and literature review

A 41-year-old man presented to us with left arm and leg weakness and mild word finding difficulties. His preoperative magnetic resonance imaging (MRI) demonstrated abnormal T1 and T2 signal changes in the right temporal lobe and basal ganglia, indicative of possible glioma. An awake craniotomy for right temporal lobectomy was performed and the tumor was resected. Full pathologic workup later revealed the patient had two distinct tumors occurring simultaneously, anaplastic astrocytoma and astroblastoma. We review the literature regarding the treatment of anaplastic astrocytoma and astroblastoma and discuss their co-occurrence.

Patterns of care and treatment outcomes of patients with astroblastoma: a National Cancer Database analysis

AIM

To evaluate the use of chemotherapy and radiation, and their outcomes for patients with astroblastoma.

PATIENTS & METHODS

This is a retrospective review of patients extracted from the National Cancer Database. We investigated overall survival (OS) using Kaplan-Meier curves. Cox proportional hazards models were used to correlate OS with risk variables and treatments.

RESULTS

OS at 5 years was 79.5%. Patients with high-grade tumors were more likely to receive chemotherapy and radiation. Patients with high-grade astroblastoma who did not receive adjuvant radiation had poor survival.

CONCLUSION

Patients with astroblastoma should be treated with curative intent. Radiation is likely beneficial in high-grade astroblastoma. The exact role of radiation and chemotherapy following surgical resection warrant further investigation.

Astroblastoma: a distinct tumor entity characterized by alterations of the X chromosome and MN1 rearrangement

Astroblastoma is a rare, enigmatic tumor of the central nervous system (CNS) which shares some clinicopathologic aspects with other CNS tumors, especially ependymoma. To further clarify the nature of astroblastoma, we performed clinicopathologic and molecular genetic studies on eight cases of astroblastoma. The median age of the patients was 14.5 years, ranging from 5 to 60 years, and seven of the patients were female. All tumors arose in the cerebral hemisphere and radiologically appeared to be well-bordered, nodular tumors often associated with cystic areas and contrast-enhancement. Six of the seven patients with prognosis data survived without recurrences during the follow-up periods ranging from six to 76 months. One patient had multiple recurrences and died six years later. All tumors exhibited salient microscopic features, such as being well demarcated from the surrounding brain tissue, perivascular arrangement of epithelioid tumor cells (represented by "astroblastic" pseudorosettes, trabecular alignment, and pseudopapillary patterns), and hyalinized blood vessels. Immunoreactivity for GFAP, S-100 protein, Olig2, and EMA was variably demonstrated in all tumors, and IDH1 R132H and L1CAM were negative. Array comparative genomic hybridization revealed numerous heterozygous deletions on chromosome X in the four tumors studied, and break-apart fluorescence in situ hybridization demonstrated rearrangement of MN1 in five tumors with successful testing. The characteristic clinicopathologic and genetic findings support the idea that astroblastoma is distinct from other CNS tumors, in particular, ependymoma. In addition, MN1 rearrangement and aberrations of chromosome X may partly be involved in the pathogenesis of astroblastoma.

Astroblastoma in a Young Female Patient: A Case Report and Literature Review of Clinicopathological, Radiological and Prognostic Characteristics and Current Treatment Strategies

Astroblastoma is an uncommon glial tumor with predominant manifestation in the young age. Herein, we report a case of 18-year-old astroblastoma female patient who presented with history of two months headache. Magnetic resonance imaging (MRI) of the brain demonstrated well circumscribed, intra-axial abnormal signal intensity lesion (size=5×4 cm²) in the right parieto-occipital region of the brain. The patient underwent complete surgical resection of the gross tumor, as confirmed by an early post-surgical MRI (i.e., within 24 hours of surgery). Histopathological examination revealed neoplastic lesion exhibiting perivascular pseudo-rosettes with centrally hyalinized blood vessel and focal nuclear pleomorphism. Immunohistochemistry staining illustrated reactivity for glial fibrillary acidic protein and integrase interactor 1 (INI-1). These features rendered the diagnosis of astroblastoma. A comprehensive review of the current literature to summarize the clinicopathological and radiological characteristics, prognostic factors and current treatment strategies of astroblastomas is also presented. Our study would expand the pool of this uncommon tumor towards its better understanding and optimal treatment.

Multimodal molecular analysis of astroblastoma enables reclassification of most cases into more specific molecular entities

Astroblastoma is a rare and controversial glioma with variable clinical behavior. The diagnosis currently rests on histologic findings of a circumscribed glioma with astroblastomatous pseudorosettes and vascular hyalinization. Immunohistochemical studies have suggested different oncogenic drivers, such as BRAF p.V600E, but very few cases have been studied using genome-wide methodologies. Recent genomic profiling identified a subset of CNS embryonal tumors with astroblastoma-like morphology that harbored MN1 gene fusions, termed "CNS high-grade neuroepithelial tumors with MN1 alteration" (CNS-HGNET-MN1). To further characterize the genetic alterations that drive astroblastomas, we performed targeted next-generation sequencing (NGS) of 500 cancer-associated genes in a series of eight cases. We correlated these findings with break-apart fluorescence in situ hybridization (FISH) analysis of the MN1 locus and genome-wide DNA methylation profiling. Four cases showed MN1 alteration by FISH, including two pediatric cases that lacked other pathogenic alterations, and two adult cases that harbored other cancer-associated gene mutations or copy number alterations (eg, CDKN2A/B homozygous deletion, TP53, ATM and TERT promoter mutations). Three of these cases grouped with the CNS-HGNET-MN1 entity by methylation profiling. Two of four MN1 intact cases by FISH showed genetic features of either anaplastic pleomorphic xanthoastrocytoma (BRAF p.V600E mutation, CDKN2A/B homozygous deletion and TERT promoter mutation) or IDH-wildtype glioblastoma (trisomy 7, monosomy 10, CDK4 amplification and TP53, NRAS and TERT promoter mutations) and these cases had an aggressive clinical course. Two clinically indolent cases remained unclassifiable despite multimodal molecular analysis. We conclude that astroblastoma histology is not specific for any entity including CNS-HGNET-MN1, and that additional genetic characterization should be considered for astroblastomas, as a number of these tumors likely contain a methylation profile or genetic alterations that suggest classification as other tumor entities. Our heterogeneous molecular findings help to explain the clinical unpredictability of astroblastoma.

Patterns of care and survival outcomes in patients with astroblastoma: an individual patient data analysis of 152 cases

BACKGROUND

Astroblastoma (AB) is a rare tumor with significant dilemma regarding diagnostic criteria, behavior, and optimum treatment.

MATERIALS AND METHODS

We searched PubMed, Google Search, and Cochrane Library for eligible studies with the following search words: astroblastoma, high-grade astroblastoma, and anaplastic astroblastoma till July 1, 2016, published in English language and collected data regarding age, sex, site of disease, pathological grade, treatment received, and survival.

RESULTS

Data of 152 patients were retrieved from 63 publications. Median age was 16 years (range 0-71). Females were affected twice more frequently than male (70.3 vs. 29.7%). Tumors were most commonly located in the frontal (39%) followed by parietal lobe (26.7%). Fifty-two and 25% of the patients had headache and seizure at presentation, 76.3% of the patients underwent a gross total resection, 41 out of 89 had a high-grade tumor, and 56 patients received adjuvant radiation with a median dose of 54 Gy (range 20-72). Adjuvant chemotherapy was used in 23 patients. Temozolomide was the most common drug used in 30% of the patients. A combination of cisplatin, etoposide with vincristine, or ifosfamide was used in 17%. Median follow-up duration was 37 months (range 1-238). Median progression-free survival and OS were 36 and 184 months, respectively. Patients with a higher-grade tumor had significantly worse OS with HR 5.260 and p = 0.001. Forty patients experienced local progression. Sixty-five percent patients underwent surgery while 50% underwent radiation as salvage.

CONCLUSION

AB has two distinct grades with higher-grade tumors having significantly poor survival. Maximal safe surgery followed by adjuvant radiation and temozolomide should be advocated for these tumors.

Prevalence and clinicopathological features of H3.3 G34-mutant high-grade gliomas: a retrospective study of 411 consecutive glioma cases in a single institution

A recurrent glycine-to-arginine/valine alteration at codon 34 (G34R/V) within H3F3A, a gene that encodes the replication-independent histone variant H3.3, reportedly occurs exclusively in pediatric glioblastomas. However, the clinicopathological and biological significances of this mutation have not been completely elucidated; especially, no such data exist for tumor samples from Japanese patients. We analyzed 411 consecutive glioma cases representing patients of all ages. Our results demonstrated that 14 patients (3.4%) harbored H3F3A mutations, of which four had G34R mutations and 10 had K27M mutations. G34R-mutant tumors were located in the parietal region in two patients and the basal ganglia in one patient. One patient showed multi-lobular extension similar to the pattern observed in gliomatosis cerebri. Regarding neuroradiological features, intratumoral calcification was evident in two cases and all cases showed no or scarce contrast enhancement on MRI. Histopathologically, the four G34R-mutant cases included three glioblastomas and one astroblastoma. We have also investigated alterations in histone methylation including H3K27me3, H3K9me3, and H3K4me3 in G34R-mutant samples by immunohistochemistry. These results indicate that G34R-mutant tumors are likely to show extensive infiltration and alterations in global histone trimethylation might also play an important role in G34R mutant tumors.

A comprehensive analysis identifies BRAF hotspot mutations associated with gliomas with peculiar epithelial morphology

Brain tumors harbor various BRAF alterations, the vast majority of which are the BRAF kinase-activating V600E mutation. BRAF mutations are most frequently detected in certain subtypes of low-grade glioma, such as pilocytic astrocytoma (PA), pleomorphic xanthoastrocytoma (PXA), ganglioglioma (GG) and dysembryoplastic neuroepithelial tumor (DNT). However, it is unclear whether gliomas harboring BRAF mutations can be invariably regarded as these glioma subtypes or their derivatives. To address this question, we analyzed 274 gliomas in our institutional case series. We performed high-resolution melting analyses and subsequent direct Sanger sequencing on DNA isolated from snap-frozen tumor tissues. As expected, BRAF mutations were detected in the aforementioned low-grade gliomas: in 4/27 PAs, 2/3 PXAs, 4/8 GGs, and 1/6 DNTs. In addition to these gliomas, 1/2 astroblastomas (ABs) and 2/122 glioblastomas (GBs) harbored BRAF mutations. Pathological investigation of the two GBs revealed that one was a GB displaying epithelial features that presumably arose from a precedent GG, whereas the other GB, which harbored a rare G596 A mutation, showed marked epithelial features, including astroblastic rosettes. Our results indicate that in addition to being present in established BRAF-associated gliomas, BRAF mutations might be associated with epithelial features in high-grade gliomas, including sheet-like arrangement of polygonal tumor cells with a plump cytoplasm and astroblastic rosettes, and thus could potentially serve as a genetic marker for these features.