The 2021 World Health Organization Classification of Tumors of the Central Nervous System: What Neuroradiologists Need to Know.

Neuroradiologists play a key role in brain tumor diagnosis and management. Staying current with the latest classification systems and diagnostic markers is important to provide optimal patient care. Publication of the 2016 World Health Organization Classification of Tumors of the Central Nervous System introduced a paradigm shift in the diagnosis of CNS neoplasms. For the first time, both histologic features and genetic alterations were incorporated into the diagnostic framework, classifying and grading brain tumors. The newly published 2021 World Health Organization Classification of Tumors of the Central Nervous System, May 2021, 5th edition, has added even more molecular features and updated pathologic diagnoses. We present, summarize, and illustrate the most salient aspects of the new 5th edition. We have selected the key "must know" topics for practicing neuroradiologists.

Gain of chromosome arm 1q in atypical meningioma correlates with shorter progression-free survival.

AIMS: Atypical (World Health Organization grade II) meningiomas have moderately high recurrence rates; even for completely resected tumours, approximately one-third will recur. Post-operative radiotherapy may aid local control and improve survival, but carries the risk of side effects. More accurate prediction of recurrence risk is therefore needed for patients with atypical meningioma. Previously, we used high-resolution array comparative genomic hybridization to identify genetic variations in 47 primary atypical meningiomas and found that approximately 60% of tumours show gain of 1q at 1q25.1 and 1q25.3 to 1q32.1 and that 1q gain appeared to correlate with shorter progression-free survival. This study aimed to validate and extend these findings in an independent sample. METHODS: Eighty-six completely resected atypical meningiomas (with 25 recurrences) from two neurosurgical centres in Ireland were identified and clinical follow-up was obtained. Utilizing a dual-colour interphase fluorescence in situ hybridization assay, 1q gain was assessed using Bacterial Artificial Chromosome probes directed against 1q25.1 and 1q32.1. RESULTS: The results confirm the high prevalence of 1q gain at these loci in atypical meningiomas. We further show that gain at 1q32.1 and age each correlate with progression-free survival in patients who have undergone complete surgical resection of atypical meningiomas. CONCLUSIONS: These independent findings suggest that assessment of 1q copy number status can add clinically useful information for the management of patients with atypical meningiomas.

Human stem cells expressing novel TSP-1 variant have anti-angiogenic effect on brain tumors.

Novel therapeutic agents combined with innovative modes of delivery and non-invasive imaging of drug delivery, pharmacokinetics and efficacy are crucial in developing effective clinical anticancer therapies. In this study, we have created and characterized multiple novel variants of anti-angiogenic protein thrombospondin (aaTSP-1) that comprises unique regions of three type-I-repeats of TSP-1 and used engineered human neural stem cells (hNSC) to provide sustained on-site delivery of secretable aaTSP-1 to tumor-vasculature. We show that hNSC-aaTSP-1 has anti-angiogenic effect on human brain and dermal microvascular endothelial cells co-cultured with established glioma cells and CD133+ glioma-initiating cells. Using human glioma cells and hNSC engineered with different combinations of fluorescent and bioluminescent marker proteins and employing multi-modality imaging techniques, we show that aaTSP-1 targets the vascular-component of gliomas and a single administration of hNSC-aaTSP-1 markedly reduces tumor vessel-density that results in inhibition of tumor-progression and increased survival in mice bearing highly malignant human gliomas. We also show that therapeutic hNSC do not proliferate and remain in an un-differentiated state in the brains of glioma-bearing mice. This study provides a platform for accelerated development of future cell-based therapies for cancer.

Downregulation of RUNX3 and TES by hypermethylation in glioblastoma.

Glioblastoma, the most aggressive and least treatable form of malignant glioma, is the most common human brain tumor. Although many regions of allelic loss occur in glioblastomas, relatively few tumor suppressor genes have been found mutated at such loci. To address the possibility that epigenetic alterations are an alternative means of glioblastoma gene inactivation, we coupled pharmacological manipulation of methylation with gene profiling to identify potential methylation-regulated, tumor-related genes. Duplicates of three short-term cultured glioblastomas were exposed to 5 microM 5-aza-dC for 96 h followed by cRNA hybridization to an oligonucleotide microarray (Affymetrix U133A). We based candidate gene selection on bioinformatics, reverse transcription-polymerase chain reaction (RT-PCR), bisulfite sequencing, methylation-specific PCR and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Two genes identified in this manner, RUNX3 and Testin (TES), were subsequently shown to harbor frequent tumor-specific epigenetic alterations in primary glioblastomas. This overall approach therefore provides a powerful means to identify candidate tumor-suppressor genes for subsequent evaluation and may lead to the identification of genes whose epigenetic dysregulation is integral to glioblastoma tumorigenesis.

Molecular analysis of astrocytomas presenting after age 10 in individuals with NF1.

BACKGROUND: Fifteen to 20% of children with neurofibromatosis type 1 (NF1) develop low-grade astrocytomas. Although brain tumors are less common in teenagers and adults with NF1, recent studies have suggested that patients with NF1 are at a significantly increased risk of developing astrocytomas. OBJECTIVE: S: To investigate the genetic basis for astrocytoma development in patients with NF1 beyond the first decade of life. METHODS: The authors performed molecular genetic analyses of 10 NF1-associated astrocytomas representing all World Health Organization (WHO) malignancy grades using fluorescence in situ hybridization, loss of heterozygosity, immunohistochemistry, and direct sequencing. RESULTS: Later-onset NF1-associated astrocytomas, unlike histologically identical sporadic astrocytomas, exhibit NF1 inactivation, supporting a direct association with NF1 rather than a chance occurrence. Furthermore, some of these astrocytomas have homozygous NF1 deletion. In addition, genetic changes observed in high-grade sporadic astrocytomas, including TP53 mutation and CDKN2A/p16 deletion, are also seen in NF1-associated high-grade astrocytomas. CONCLUSIONS: Neurofibromatosis type 1-associated astrocytomas occurring in patients older than 10 years exhibit genetic changes observed in sporadic high-grade astrocytomas. Patients with neurofibromatosis type 1 and germline NF1 deletions may be at risk for developing late-onset astrocytomas.

Development of a novel non-human primate model for preclinical gene vector safety studies. Determining the effects of intracerebral HSV-1 inoculation in the common marmoset: a comparative study.

The owl monkey (Aotus trivirgatus) has served as the standard non-human primate model of herpes simplex virus-1 (HSV-1) infection because it is highly susceptible to HSV-1 encephalitis. Owl monkeys, however, are expensive, difficult to obtain, and difficult to maintain in captivity, thus greatly hampering the efficiency of preclinical gene therapy trials for brain tumors using HSV-1-based vectors. We have therefore compared the susceptibility of the common marmoset (Callithrix jacchus) with the owl monkey in a model of intracerebral inoculation of wildtype HSV-1 F-strain at increasing titers. The common marmosets consistently succumbed earlier to viral encephalitis than the owl monkeys. The histological evaluation of the common marmoset revealed extensive HSV-1 infection with a concomitant yet less marked inflammatory response compared to the owl monkeys. PCR for HSV-1 demonstrated a similar extra-CNS shedding route in both experimental models. Our findings show that the common marmoset is at least as susceptible to intracerebral HSV-infection as the owl monkey and that it can therefore serve as a valid and reliable experimental model for the important preclinical safety tests of HSV-based therapeutic viral vector constructs in the brain.

Familial schwannomatosis: exclusion of the NF2 locus as the germline event.

BACKGROUND: Schwannomatosis is a recently recognized disorder, defined as multiple pathologically proven schwannomas without vestibular tumors diagnostic of neurofibromatosis 2 (NF2). Some investigators have questioned whether schwannomatosis is merely an attenuated form of NF2. METHODS: The authors identified eight families in which a proband met their diagnostic criteria for schwannomatosis. Archived and prospectively acquired tumor specimens were studied by mutational analysis at the NF2 locus, loss of heterozygosity analysis along chromosome 22, and fluorescent in situ hybridization analysis of NF2 and the more centromeric probe BCR. Linkage analysis could be performed in six of eight families. RESULTS: Clinical characterization of these kindreds showed that no affected family member harbored a vestibular tumor. Molecular analysis of 28 tumor specimens from 17 affected individuals in these kindreds revealed a pattern of somatic NF2 inactivation incompatible with our current understanding of NF2 as an inherited tumor suppressor gene syndrome. Linkage analysis excluded the NF2 locus in two kindreds, and showed a maximum lod score of 6.60 near the more centromeric marker D22S1174. CONCLUSIONS: Schwannomatosis shows clinical and molecular differences from NF2 and should be considered a third major form of neurofibromatosis. Further work is needed to identify the inherited genetic element responsible for familial schwannomatosis.

Clear cell pleomorphic xanthoastrocytoma: case report.

Pleomorphic xanthoastrocytoma (PXA) is a well-described astrocytic neoplasm with distinctive clinical and pathological features. Although most patients with PXAs are cured by surgical excision, other patients experience malignant progression and tumor recurrence. We describe a 47-year-old woman with a left temporal lobe PXA that had classic histopathological characteristics as well as extensive clear cell and focal papillary changes, and some anaplastic findings. The patient has now suffered two recurrences after complete resection. The case illustrates a rare, previously undescribed histological variant of PXA, with a prominent clear cell and focal papillary morphology. The study of histologically similar cases is needed to determine whether this variant is always associated with a greater likelihood of recurrence.

Tumor location and growth pattern correlate with genetic signature in oligodendroglial neoplasms.

Molecular genetic subsets of anaplastic oligodendroglioma behave in biologically distinct ways, in both their rates of growth and their responses to standard therapies. In a series of 64 cases, we evaluated whether allelic loss of chromosomal arms 1p and 19q, an early molecular event in the genesis of chemosensitive oligodendrogliomas, is related to tumor location and extent of tumor spread in the brain. We observed that tumor genotype was closely associated with tumor location (P < 0.001). Anaplastic oligodendrogliomas located in the frontal, parietal, and occipital lobes were significantly more likely to harbor allelic loss of chromosomal arms 1p and 19q than histologically indistinguishable tumors arising in the temporal lobe, insula, and diencephalon (P < 0.001). In addition, loss of heterozygosity for 1p and 19q was significantly associated with a bilateral pattern of growth (P = 0.037); all seven bilaterally distributed anaplastic oligodendrogliomas had 1p and 19q allelic loss. We conclude, therefore, that molecular subtypes of oligodendrogliomas may arise preferentially in certain lobes of the brain and have differential patterns of growth, with tumors having allelic loss of chromosomes 1p and 19q occurring most frequently in the frontal lobes and having a tendency for widespread growth across the midline. These findings encourage inquiries into the biological basis of such marked differences and already have implications for the current management of these neoplasms.

Oligodendrocyte lineage genes (OLIG) as molecular markers for human glial brain tumors.

The most common primary tumors of the human brain are thought to be of glial cell origin. However, glial cell neoplasms cannot be fully classified by cellular morphology or with conventional markers for astrocytes, oligodendrocytes, or their progenitors. Recent insights into central nervous system tumorigenesis suggest that novel molecular markers might be found among factors that have roles in glial development. Oligodendrocyte lineage genes (Olig1/2) encode basic helix-loop-helix transcription factors. In the rodent central nervous system, they are expressed exclusively in oligodendrocytes and oligodendrocyte progenitors, and Olig1 can promote formation of an chondroitin sulfate proteoglycon-positive glial progenitor. Here we show that human OLIG genes are expressed strongly in oligodendroglioma, contrasting absent or low expression in astrocytoma. Our data provide evidence that neoplastic cells of oligodendroglioma resemble oligodendrocytes or their progenitor cells and may derive from cells of this lineage. They further suggest the diagnostic potential of OLIG markers to augment identification of oligodendroglial tumors.

PDGF autocrine stimulation dedifferentiates cultured astrocytes and induces oligodendrogliomas and oligoastrocytomas from neural progenitors and astrocytes in vivo.

We present evidence that some low-grade oligodendrogliomas may be comprised of proliferating glial progenitor cells that are blocked in their ability to differentiate, whereas malignant gliomas have additionally acquired other mutations such as disruption of cell cycle arrest pathways by loss of Ink4a-Arf. We have modeled these effects in cell culture and in mice by generating autocrine stimulation of glia through the platelet-derived growth factor receptor (PDGFR). In cell culture, PDGF signaling induces proliferation of glial precursors and blocks their differentiation into oligodendrocytes and astrocytes. In addition, coexpression of PDGF and PDGF receptors has been demonstrated in human gliomas, implying that autocrine stimulation may be involved in glioma formation. In this study, using somatic cell type-specific gene transfer we investigated the functions of PDGF autocrine signaling in gliomagenesis by transferring the overexpression of PDGF-B into either nestin-expressing neural progenitors or glial fibrillary acidic protein (GFAP)-expressing astrocytes both in cell culture and in vivo. In cultured astrocytes, overexpression of PDGF-B caused significant increase in proliferation rate of both astrocytes and neural progenitors. Furthermore, PDGF gene transfer converted cultured astrocytes into cells with morphologic and gene expression characteristics of glial precursors. In vivo, gene transfer of PDGF to neural progenitors induced the formation of oligodendrogliomas in about 60% of mice by 12 wk of age; PDGF transfer to astrocytes induced the formation of either oligodendrogliomas or mixed oligoastrocytomas in about 40% of mice in the same time period. Loss of Ink4a-Arf, a mutation frequently found in high-grade human gliomas, resulted in shortened latency and enhanced malignancy of gliomas. The highest percentage of PDGF-induced malignant gliomas arose from of Ink4a-Arf null progenitor cells. These data suggest that chronic autocrine PDGF signaling can promote a proliferating population of glial precursors and is potentially sufficient to induce gliomagenesis. Loss of Ink4a-Arf is not required for PDGF-induced glioma formation but promotes tumor progression toward a more malignant phenotype.

Selective inactivation of p53 facilitates mouse epithelial tumor progression without chromosomal instability.

We examined the selective pressure for, and the impact of, p53 inactivation during epithelial tumor evolution in a transgenic brain tumor model. In TgT(121) mice, cell-specific inactivation of the pRb pathway in brain choroid plexus epithelium initiates tumorigenesis and induces p53-dependent apoptosis. We previously showed that p53 deficiency accelerates tumor growth due to diminished apoptosis. Here we show that in a p53(+/-) background, slow-growing dysplastic tissue undergoes clonal progression to solid angiogenic tumors in all animals. p53 is inactivated in all progressed tumors, with loss of the wild-type allele occurring in 90% of tumors. Moreover, similar progression occurs in 38% of TgT(121)p53(+/+) mice, also with loss of at least one p53 allele and inactivation of p53. Thus, the selective pressure for p53 inactivation, likely based on its apoptotic function, is high. Yet, in all cases, p53 inactivation correlates with progression beyond apoptosis reduction, from dysplasia to solid vascularized tumors. Hence, p53 suppresses tumor progression in this tissue by multiple mechanisms. Previous studies of fibroblasts and hematopoietic cells show that p53 deficiency can be associated with chromosomal instability, a mechanism that may drive tumor progression. To determine whether genomic gains or losses are present in tumors that progress in the absence of p53, we performed comparative genomic hybridization analysis. Surprisingly, the only detectable chromosomal imbalance was partial or complete loss of chromosome 11, which harbors the p53 gene and is thus the selected event. Flow cytometry confirmed that the majority of tumor cells were diploid. These studies indicate that loss of p53 function is frequent under natural selective pressures and furthermore that p53 loss can facilitate epithelial tumor progression by a mechanism in addition to apoptosis reduction and distinct from chromosomal instability.

PTEN is a target of chromosome 10q loss in anaplastic oligodendrogliomas and PTEN alterations are associated with poor prognosis.

Allelic loss of 10q is a common genetic event in malignant gliomas, with three 10q tumor suppressor genes, ERCC6, PTEN, and DMBT1, putatively implicated in the most common type of malignant glioma, glioblastoma. Anaplastic oligodendroglioma, another type of malignant glioma, provides a unique opportunity to study the relevance of particular genetic alterations to chemosensitivity and survival. We therefore analyzed these three genes in 72 anaplastic oligodendrogliomas. Deletion mapping demonstrated 10q loss in 14 of 67 informative cases, with the PTEN and DMBT1 regions involved in all deletions but with the ERCC6 locus spared in two cases. Seven tumors had PTEN gene alterations; two had homozygous DMBT1 deletions, but at least one reflected unmasking of a germline DMBT1 deletion. No mutations were found in ERCC6 exon 2. Chemotherapeutic response occurred in two of the seven tumors with PTEN alterations, but with unexpected short survival times. PTEN gene alterations were not associated with poor therapeutic response in multivariate analysis, but were independently predictive of poor prognosis even after multivariate adjustment for both 10q and 1p loss. In anaplastic oligodendroglioma, therefore, PTEN is a target of 10q loss, and PTEN alterations are associated with poor prognosis, even in chemosensitive cases.

Survey of somatic mutations in tuberous sclerosis complex (TSC) hamartomas suggests different genetic mechanisms for pathogenesis of TSC lesions.

Tuberous sclerosis complex (TSC), an autosomal dominant disease caused by mutations in either TSC1 or TSC2, is characterized by the development of hamartomas in a variety of organs. Concordant with the tumor-suppressor model, loss of heterozygosity (LOH) is known to occur in these hamartomas at loci of both TSC1 and TSC2. LOH has been documented in renal angiomyolipomas (AMLs), but loss of the wild-type allele in cortical tubers appears to be very uncommon. Analysis of second, somatic events in tumors for which the status of both TSC1 and TSC2 is known is essential for exploration of the pathogenesis of TSC-lesion development. We analyzed 24 hamartomas from 10 patients for second-hit mutations, by several methods, including LOH, scanning of all exons of both TSC1 and TSC2, promoter methylation of TSC2, and clonality analysis. Our results document loss of the wild-type allele in six of seven AMLs, without evidence of the inactivation of the second allele in many of the other lesions, including tumors that appear to be clonally derived. Laser-capture microdissection further demonstrated loss of the second allele in all three cellular components of an AML. This study thus provides evidence that, in both TSC1 and TSC2, somatic mutations resulting in the loss of wild-type alleles may not be necessary in some tumor types-and that other mechanisms may contribute to tumorigenesis in this setting.