Glioblastomas harboring gene fusions detected by next-generation sequencing

Clinical, pathologic, and genomic characteristics of two pediatric glioneuronal tumors with a CLIP2::MET fusion

Integration of molecular data with histologic, radiologic, and clinical features is imperative for accurate diagnosis of pediatric central nervous system (CNS) tumors. Whole transcriptome RNA sequencing (RNAseq), a genome-wide and non-targeted approach, allows for the detection of novel or rare oncogenic fusion events that contribute to the tumorigenesis of a substantial portion of pediatric low- and high-grade glial and glioneuronal tumors. We present two cases of pediatric glioneuronal tumors occurring in the occipital region with a CLIP2::MET fusion detected by RNAseq. Chromosomal microarray studies revealed copy number alterations involving chromosomes 1, 7, and 22 in both tumors, with Case 2 having an interstitial deletion breakpoint in the CLIP2 gene. By methylation profiling, neither tumor had a match result, but both clustered with the low-grade glial/glioneuronal tumors in the UMAP. Histologically, in both instances, our cases displayed characteristics of a low-grade tumor, notably the absence of mitotic activity, low Ki-67 labeling index and the lack of necrosis and microvascular proliferation. Glial and neuronal markers were positive for both tumors. Clinically, both patients achieved clinical stability post-tumor resection and remain under regular surveillance imaging without adjuvant therapy at the last follow-up, 6 months and 3 years, respectively. This is the first case report demonstrating the presence of a CLIP2::MET fusion in two pediatric low-grade glioneuronal tumors (GNT). Conservative clinical management may be considered for patients with GNT and CLIP2:MET fusion in the context of histologically low-grade features.

Pediatric CNS tumors and 2021 WHO classification: what do oncologists need from pathologists?

The fifth edition of the WHO Classification of Tumors of the Central Nervous System (CNS), published in 2021, established new approaches to both CNS tumor nomenclature and grading, emphasizing the importance of integrated diagnoses and layered reports. This edition increased the role of molecular diagnostics in CNS tumor classification while still relying on other established approaches such as histology and immunohistochemistry. Moreover, it introduced new tumor types and subtypes based on novel diagnostic technologies such as DNA methylome profiling. Over the past decade, molecular techniques identified numerous key genetic alterations in CSN tumors, with important implications regarding the understanding of pathogenesis but also for prognosis and the development and application of effective molecularly targeted therapies. This review summarizes the major changes in the 2021 fifth edition classification of pediatric CNS tumors, highlighting for each entity the molecular alterations and other information that are relevant for diagnostic, prognostic, or therapeutic purposes and that patients' and oncologists' need from a pathology report.

Next-Generation Sequencing of Vitreoretinal Lymphoma by Vitreous Liquid Biopsy: Diagnostic Potential and Genotype/Phenotype Correlation

Purpose

To determine the diagnostic potential of next-generation sequencing (NGS) in vitreous samples, analyze genotype-phenotype characteristics, and compare NGS of matched vitreous and brain samples in patients with associated central nervous system lymphoma (CNSL).

Methods

A total of 32 patients suspected of vitreoretinal lymphoma (VRL) who underwent diagnostic vitrectomy and NGS were included in this retrospective observational case-series. Fresh vitreous specimens from diagnostic vitrectomy of VRL-suspected patients underwent NGS using a custom panel targeting 747 candidate genes for lymphoma. They also underwent malignancy cytology, interleukin (IL)-10/IL-6, immunoglobulin heavy chain (IGH)/immunoglobulin kappa light chain (IGK) monoclonality testing. MYD88 L265P mutation was examined from anterior chamber tap samples. The diagnosis of VRL was made based on typical clinical characteristics for VRL, as well as malignant cytology, IGH/IGK clonality, or IL-10/IL-6 > 1. Sensitivity and specificity of NGS were compared with conventional diagnostic tests. Brain tissues suspected of lymphoma were collected by stereotactic biopsy and underwent NGS. Genetic variations detected in NGS of vitreous and brain tissue specimens were compared.

Results

The sensitivity values for cytology, IL-10/IL-6 > 1, clonality assays for IGH and IGK, MYD88 L265P detection in anterior chamber tap samples, and vitreous NGS were 0.23, 0.83, 0.68, 0.79, 0.67, and 0.85, with specificity values of 1.00, 0.83, 0.50, 0.25, 0.83, and 0.83, respectively. The sensitivity (0.85) of vitreous NGS was the highest compared to other conventional diagnostic tests for VRL. The most common mutations were MYD88 (91%), CDKN2A (36%), PIM1 (32%), IGLL5 (27%), and ETV6 (23%). Although several gene alterations demonstrated heterogeneity between the brain and eyes, some common mutational profiles were observed in matched vitreous and brain samples.

Conclusions

Overall, NGS of the vitreous demonstrated high sensitivity among conventional diagnostic tests. VRL and CNSL appeared to have both shared and distinct genetic variations, which may suggest site-specific variations from a common origin.

Synthesis and Biological Evaluation of a Library of Sulfonamide Analogs of Memantine to Target Glioblastoma

A library of 34 lipophilic sulfonamides based upon the memantine core has been synthesized to identify potential drug candidates to cross the blood-brain barrier and target glioblastoma. The library was screened for in vitro activity against 4 mammalian cell lines, including U-87 (glioblastoma). Additional synthetic variation of the active compounds has validated the importance of specific regions of the pharmacophore, with the sulfonamide functionality and S-aryl unit displaying the most significant impact. In silico investigations suggest the active compounds might target DDR1 or RET proteins. The investigation has resulted in several compounds that warrant further development for lead optimization.

RNA fusion transcript panel identifies diverse repertoire of fusions in adult glioma patients with therapeutic implications

Background

Recurrent gliomas are therapeutically challenging diseases with few treatment options available. One area of potential therapeutic vulnerability is the presence of targetable oncogenic fusion proteins.

Methods

To better understand the clinical benefit of routinely testing for fusion proteins in adult glioma patients, we performed a retrospective review of 647 adult patients with glioma who underwent surgical resection at our center between August 2017 and May 2021 and whose tumors were analyzed with an in-house fusion transcript panel.

Results

Fifty-two patients (8%) were found to harbor a potentially targetable fusion with 11 (21%) of these patients receiving treatment with a fusion-targeted inhibitor. The targetable genes found to be involved in a fusion included FGFR3, MET, EGFR, NTRK1, NTRK2, BRAF, ROS1, and PIK3CA.

Conclusions

This analysis demonstrates that routine clinical testing for gene fusions identifies a diverse repertoire of potential therapeutic targets in adult patients with glioma and can offer rational therapeutic options for patients with recurrent disease.

Diagnosis and management of complications from the treatment of primary central nervous system tumors in adults

Central nervous system (CNS) tumor patients commonly undergo multimodality treatment in the course of their disease. Adverse effects and complications from these interventions have not been systematically studied, but pose significant challenges in clinical practice and impact function and quality of life, especially in the management of long-term brain tumor survivors. Here, the European Association of Neuro-Oncology (EANO) has developed recommendations to prevent, diagnose, and manage adverse effects and complications in the adult primary brain CNS tumor (except lymphomas) patient population with a specific focus on surgery, radiotherapy, and pharmacotherapy. Specifically, we also provide recommendations for dose adaptations, interruptions, and reexposure for pharmacotherapy that may serve as a reference for the management of standard of care in clinical trials. We also summarize which interventions are unnecessary, inactive or contraindicated. This consensus paper should serve as a reference for the conduct of standard therapy within and outside of clinical trials.

Role of Molecular Targeted Therapeutic Drugs in Treatment of Glioblastoma: A Review Article

Glioblastoma is remarkably periodic primary brain tumor, characterizing an eminently heterogeneous pattern of neoplasms that are utmost destructive and threatening cancers. An enhanced and upgraded knowledge of the various molecular pathways that cause malignant changes in glioblastoma has resulted in advancement of numerous biomarkers and the interpretation of various agents that pointedly target tumor cells and microenvironment. In this review, literature or information on various targeted therapy for glioblastoma is discussed. English language articles were scrutinized in plentiful directory or databases like PubMed, ScienceDirect, Web of Sciences, Google Scholar, and Scopus. The important keywords used for searching databases are "Glioblastoma," "Targeted therapy in glioblastoma," "Therapeutic drugs in glioblastoma," and "Molecular targets in glioblastoma."

Protein Tyrosine Phosphatase Receptor Zeta 1 as a Potential Target in Cancer Therapy and Diagnosis

Protein tyrosine phosphatase receptor zeta 1 (PTPRZ1) is a type V transmembrane tyrosine phosphatase that is highly expressed during embryonic development, while its expression during adulthood is limited. PTPRZ1 is highly detected in the central nervous system, affecting oligodendrocytes' survival and maturation. In gliomas, PTPRZ1 expression is significantly upregulated and is being studied as a potential cancer driver and as a target for therapy. PTPRZ1 expression is also increased in other cancer types, but there are no data on the potential functional significance of this finding. On the other hand, low PTPRZ1 expression seems to be related to a worse prognosis in some cancer types, suggesting that in some cases, it may act as a tumor-suppressor gene. These discrepancies may be due to our limited understanding of PTPRZ1 signaling and tumor microenvironments. In this review, we present evidence on the role of PTPRZ1 in angiogenesis and cancer and discuss the phenomenal differences among the different types of cancer, depending on the regulation of its tyrosine phosphatase activity or ligand binding. Clarifying the involved signaling pathways will lead to its efficient exploitation as a novel therapeutic target or as a biomarker, and the development of proper therapeutic approaches.

Signaling pathways in brain tumors and therapeutic interventions

Brain tumors, although rare, contribute to distinct mortality and morbidity at all ages. Although there are few therapeutic options for brain tumors, enhanced biological understanding and unexampled innovations in targeted therapies and immunotherapies have considerably improved patients' prognoses. Nonetheless, the reduced response rates and unavoidable drug resistance of currently available treatment approaches have become a barrier to further improvement in brain tumor (glioma, meningioma, CNS germ cell tumors, and CNS lymphoma) treatment. Previous literature data revealed that several different signaling pathways are dysregulated in brain tumor. Importantly, a better understanding of targeting signaling pathways that influences malignant behavior of brain tumor cells might open the way for the development of novel targeted therapies. Thus, there is an urgent need for a more comprehensive understanding of the pathogenesis of these brain tumors, which might result in greater progress in therapeutic approaches. This paper began with a brief description of the epidemiology, incidence, risk factors, as well as survival of brain tumors. Next, the major signaling pathways underlying these brain tumors' pathogenesis and current progress in therapies, including clinical trials, targeted therapies, immunotherapies, and system therapies, have been systemically reviewed and discussed. Finally, future perspective and challenges of development of novel therapeutic strategies in brain tumor were emphasized.

Detection of ROS1 gene fusions using next-generation sequencing for patients with malignancy in China

Objective: This study aimed to identify ROS1 fusion partners in Chinese patients with solid tumors. Methods: Next-generation sequencing (NGS) analysis was used to detect ROS1 rearrangement in 45,438 Chinese patients with solid tumors between 2015 and 2020, and the clinical characteristics and genetic features of gene fusion were evaluated. H&E staining of the excised tumor tissues was conducted. Samples with a tumor cell content ≥ 20% were included for subsequent DNA extraction and sequencing analysis. Results: A total of 92 patients with ROS1 rearrangements were identified using next-generation sequencing, and the most common histological type lung cancer. From the 92 ROS1 fusion cases, 24 ROS1 fusion partners had been identified, including 14 novel partners and 10 reported partners. Of these, CD74, EZR, SDC4, and TPM3 were the four most frequently occurring partners. Fourteen novel ROS1 fusion partners were detected in 16 patients, including DCBLD1-ROS1, FRK-ROS1, and VGLL2-ROS1. In many patients, the ROS1 breakpoint was located between exons 32 and 34. Conclusion: This study describes 14 novel ROS1 fusion partners based on the largest ROS1 fusion cohort, and the ROS1 breakpoint was mostly located between exons 32 and 34. Additionally, next-generation sequencing is an optional method for identifying novel ROS1 fusions.

Paediatric-type diffuse high-grade gliomas in the 5th CNS WHO Classification

As a relevant element of novelty, the fifth CNS WHO Classification highlights the distinctive pathobiology underlying gliomas arising primarily in children by recognizing for the first time the families of paediatric-type diffuse gliomas, both high-grade and low-grade. This review will focus on the family of paediatric-type diffuse high-grade gliomas, which includes four tumour types: 1) Diffuse midline glioma H3 K27-altered; 2) Diffuse hemispheric glioma H3 G34-mutant; 3) Diffuse paediatric-type high-grade glioma H3-wildtype and IDH-wildtype; and 4) Infant-type hemispheric glioma. The essential and desirable diagnostic criteria as well as the entities entering in the differential will be discussed for each tumour type. A special focus will be given on the issues encountered in the daily practice, especially regarding the diagnosis of the diffuse paediatric-type high-grade glioma H3-wildtype and IDH-wildtype. The advantages and the limits of the multiple molecular tests which may be utilised to define the entities of this tumour family will be evaluated in each diagnostic context.

Response to Selpercatinib in a Patient With Recurrent Glioblastoma and RET Amplification

Glioblastoma (GBM) is a malignant central nervous system neoplasm that remains largely incurable. Limited treatment options currently exist after disease progression on standard-of-care first-line therapy. However, repurposing the use of approved therapies in patients with potentially targetable genomic alterations continues to be an emerging area of interest. This report presents the first description of a patient with isocitrate dehydrogenase wild-type GBM with an underlying RET amplification who demonstrated a near-complete response while receiving therapy with the RET inhibitor selpercatinib. The case highlights the excellent blood-brain barrier penetration of selpercatinib, as well as its potential role in the management of RET-amplified GBM. Larger biomarker-enriched studies are needed to confirm the results of this case report. Given the rare incidence of RET alterations in GBM, findings from this report can help guide and support optimal treatment strategies for patients with RET-altered GBM.

In silico validation of RNA-Seq results can identify gene fusions with oncogenic potential in glioblastoma

RNA-Sequencing (RNA-Seq) can identify gene fusions in tumors, but not all these fusions have functional consequences. Using multiple data bases, we have performed an in silico analysis of fusions detected by RNA-Seq in tumor samples from 139 newly diagnosed glioblastoma patients to identify in-frame fusions with predictable oncogenic potential. Among 61 samples with fusions, there were 103 different fusions, involving 167 different genes, including 20 known oncogenes or tumor suppressor genes (TSGs), 16 associated with cancer but not oncogenes or TSGs, and 32 not associated with cancer but previously shown to be involved in fusions in gliomas. After selecting in-frame fusions able to produce a protein product and running Oncofuse, we identified 30 fusions with predictable oncogenic potential and classified them into four non-overlapping categories: six previously described in cancer; six involving an oncogene or TSG; four predicted by Oncofuse to have oncogenic potential; and 14 other in-frame fusions. Only 24 patients harbored one or more of these 30 fusions, and only two fusions were present in more than one patient: FGFR3::TACC3 and EGFR::SEPTIN14. This in silico study provides a good starting point for the identification of gene fusions with functional consequences in the pathogenesis or treatment of glioblastoma.

A Targeted Next-Generation Sequencing Panel to Genotype Gliomas

Gliomas account for the majority of primary brain tumors. Glioblastoma is the most common and malignant type. Based on their extreme molecular heterogeneity, molecular markers can be used to classify gliomas and stratify patients into diagnostic, prognostic, and therapeutic clusters. In this work, we developed and validated a targeted next-generation sequencing (NGS) approach to analyze variants or chromosomal aberrations correlated with tumorigenesis and response to treatment in gliomas. Our targeted NGS analysis covered 13 glioma-related genes (ACVR1, ATRX, BRAF, CDKN2A, EGFR, H3F3A, HIST1H3B, HIST1H3C, IDH1, IDH2, P53, PDGFRA, PTEN), a 125 bp region of the TERT promoter, and 54 single nucleotide polymorphisms (SNPs) along chromosomes 1 and 19 for reliable assessment of their copy number alterations (CNAs). Our targeted NGS approach provided a portrait of gliomas’ molecular heterogeneity with high accuracy, specificity, and sensitivity in a single workflow, enabling the detection of variants associated with unfavorable outcomes, disease progression, and drug resistance. These preliminary results support its use in routine diagnostic neuropathology.

Therapeutic Options in Neuro-Oncology

One of the biggest challenges in neuro-oncology is understanding the complexity of central nervous system tumors, such as gliomas, in order to develop suitable therapeutics. Conventional therapies in malignant gliomas reconcile surgery and radiotherapy with the use of chemotherapeutic options such as temozolomide, chloroethyl nitrosoureas and the combination therapy of procarbazine, lomustine and vincristine. With the unraveling of deregulated cancer cell signaling pathways, targeted therapies have been developed. The most affected signaling pathways in glioma cells involve tyrosine kinase receptors and their downstream pathways, such as the phosphatidylinositol 3-kinases (PI3K/AKT/mTOR) and mitogen-activated protein kinase pathways (MAPK). MAPK pathway inhibitors include farnesyl transferase inhibitors, Ras kinase inhibitors and mitogen-activated protein extracellular regulated kinase (MEK) inhibitors, while PI3K/AKT/mTOR pathway inhibitors are divided into pan-inhibitors, PI3K/mTOR dual inhibitors and AKT inhibitors. The relevance of the immune system in carcinogenesis has led to the development of immunotherapy, through vaccination, blocking of immune checkpoints, oncolytic viruses, and adoptive immunotherapy using chimeric antigen receptor T cells. In this article we provide a comprehensive review of the signaling pathways underlying malignant transformation, the therapies currently used in the treatment of malignant gliomas and further explore therapies under development, including several ongoing clinical trials.

Next generation sequencing in adult patients with glioblastoma in Switzerland: a multi-centre decision analysis

BACKGROUND

Glioblastoma is the most common malignant primary brain tumour in adults and driven by various genomic alterations. Next generation sequencing (NGS) provides timely information about the genetic landscape of tumours and might detect targetable mutations. To date, differences exist in the application and NGS assays used as it remains unclear to what extent these variants may affect clinical decision making. In this survey-based study, we investigated the use of NGS in adult patients with glioblastoma in Switzerland.

METHODS

All eight primary care centres for Neuro-Oncology in Switzerland participated in this survey. The NGS assays used as well as the criteria for the application of NGS in newly diagnosed glioblastoma were investigated. Decision trees were analysed for consensus and discrepancies using the objective consensus methodology.

RESULTS

Seven out of eight centres perform NGS in patients with newly diagnosed glioblastoma using custom made or commercially available assays. The criteria most relevant to decision making were age, suitability of standard treatment and fitness. NGS is most often used in fitter patients under the age of 60 years who are not suitable for standard therapy, while it is rarely performed in patients in poor general health.

CONCLUSION

NGS is frequently applied in glioblastomas in adults in Neuro-Oncology centres in Switzerland despite seldom changing the course of treatment to date.

Glioma targeted therapy: insight into future of molecular approaches

Gliomas are the common type of brain tumors originating from glial cells. Epidemiologically, gliomas occur among all ages, more often seen in adults, which males are more susceptible than females. According to the fifth edition of the WHO Classification of Tumors of the Central Nervous System (WHO CNS5), standard of care and prognosis of gliomas can be dramatically different. Generally, circumscribed gliomas are usually benign and recommended to early complete resection, with chemotherapy if necessary. Diffuse gliomas and other high-grade gliomas according to their molecule subtype are slightly intractable, with necessity of chemotherapy. However, for glioblastoma, feasible resection followed by radiotherapy plus temozolomide chemotherapy define the current standard of care. Here, we discuss novel feasible or potential targets for treatment of gliomas, especially IDH-wild type glioblastoma. Classic targets such as the p53 and retinoblastoma (RB) pathway and epidermal growth factor receptor (EGFR) gene alteration have met failure due to complex regulatory network. There is ever-increasing interest in immunotherapy (immune checkpoint molecule, tumor associated macrophage, dendritic cell vaccine, CAR-T), tumor microenvironment, and combination of several efficacious methods. With many targeted therapy options emerging, biomarkers guiding the prescription of a particular targeted therapy are also attractive. More pre-clinical and clinical trials are urgently needed to explore and evaluate the feasibility of targeted therapy with the corresponding biomarkers for effective personalized treatment options.

Grading of adult diffuse gliomas according to the 2021 WHO Classification of Tumors of the Central Nervous System

The grading of gliomas based on histological features has been a subject of debate for several decades. A consensus has not yet been reached because of technical limitations and inter-observer variations. While the traditional grading system has failed to stratify the risk of IDH-mutant astrocytoma, canonical histological and proliferative markers may be applicable to the risk stratification of IDH-wild-type astrocytoma. Numerous studies have examined molecular markers in order to obtain more clinically relevant information that will improve the risk stratification of gliomas. The CDKN2A/B homozygous deletion for IDH-mutant astrocytoma and the following three criteria for IDH-wild-type astrocytoma: the concurrent gain of whole chromosome 7 and loss of whole chromosome 10, TERT promoter mutations, and EGFR amplification, were identified as independent molecular markers of the worst clinical outcomes. Therefore, the 2021 World Health Organization (WHO) Classification of Tumors of the Central Nervous System adopted these molecular markers into the revised grading criteria of IDH-mutant and -wild-type astrocytoma, respectively, as a grading system within tumor types. Of note, several recent studies have shown that some low-grade IDH-wild-type astrocytoma lacking both the molecular glioblastoma signature and genetic alterations typical of pediatric-type gliomas may demonstrate a relatively indolent clinical course, suggesting the existence of lower-grade adult IDH-wild-type astrocytoma. In terms of oligodendroglioma, IDH-mutant, and 1p/19q codeleted, consistent makers that predict poor outcomes have not yet been identified, and, thus, the current criteria have remained unchanged. Molecular testing to fulfill the revised WHO criteria is, however, not always available worldwide, and in that case, an integrated diagnosis combining all available complementary information is highly recommended. This review discusses controversial issues surrounding legacy grading systems and newly identified potential genetic markers of adult diffuse gliomas and provides perspectives on future grading systems.

Investigating natural compounds against oncogenic RET tyrosine kinase using pharmacoinformatic approaches for cancer therapeutics

Rearranged during transfection (RET) tyrosine kinase is a transmembrane receptor tyrosine kinase regulating vital aspects of cellular proliferation, differentiation, and survival. An outstanding challenge in designing protein kinase inhibitors is due to the development of drug resistance. The “gain of function” mutations in the RET gate-keeper residue, Val804, confers resistance to the majority of known RET inhibitors, including vandetanib. To curtail this resistance, researchers developed selpercatinib (LOXO-292) against the RET gate-keeper mutant forms – V804M and V804L. In the present in silico investigation, a receptor–ligand pharmacophore model was generated to identify small molecule inhibitors effective for wild-type (WT) as well as mutant RET kinase variants. The generated model was employed to screen 144 766 natural products (NPs) available in the ZINC database and the retrieved NPs were filtered for their drug-likeness. The resulting 2696 drug-like NPs were subjected to molecular docking with the RET WT kinase domain and a total of 27 molecules displayed better dock scores than the reference inhibitors – vandetanib and selpercatinib. From 27 NPs, an aggregate of 12 compounds demonstrated better binding free energy (BFE) scores than the reference inhibitors, towards RET. Thus, the 12 NPs were also subjected to docking, simulation, and BFE estimation towards the constructed gate-keeper RET mutant structures. The BFE calculations revealed 3 hits with better BFE scores than the reference inhibitors towards WT, V804M, and V804L RET variants. Thus, the scaffolds of hit compounds presented in this study could act as potent RET inhibitors and further provide insights for drug optimization targeting aberrant activation of RET signaling, specifically the mutation of gate-keeper residue – Val804.

Identification of natural product inhibitors against rearranged during transfection (RET) tyrosine kinase as cancer therapeutics using combination of in silico techniques.

Landscape of driver gene events, biomarkers, and druggable targets identified by whole-genome sequencing of glioblastomas

BACKGROUND

The survival of glioblastoma patients is poor. Median survival after diagnosis is 15 months, despite treatment involving surgical resection, radiotherapy, and/or temozolomide chemotherapy. Identification of novel targets and stratification strategies of glioblastoma patients to improve patient survival is urgently needed. Whole-genome sequencing (WGS) is the most comprehensive means to identify such DNA-level targets. We report a unique set of WGS samples along with comprehensive analyses of the glioblastoma genome and potential clinical impact of WGS.

METHODS

Our cohort consisted of 42 glioblastoma tumor tissue and matched whole-blood samples, which were whole-genome sequenced as part of the CPCT-02 study. Somatic single-nucleotide variants, small insertions/deletions, multi-nucleotide variants, copy-number alterations (CNAs), and structural variants were analyzed. These aberrations were harnessed to investigate driver genes, enrichments in CNAs, mutational signatures, fusion genes, and potential targeted therapies.

RESULTS

Tumor mutational burden (TMB) was similar to other WGS efforts (1-342 mutations per megabase pair). Mutational analysis in low TMB samples showed that the age-related CpG demethylation signature was dominant, while hyper- and ultramutated tumors had additional defective DNA mismatch repair signatures and showed microsatellite instability in their genomes. We detected chromothripsis in 24% of our cohort, recurrently on chromosomes 1 and 12. Recurrent noncoding regions only resulted in TERT promoter variants. Finally, we found biomarkers and potentially druggable changes in all but one of our tumor samples.

CONCLUSIONS

With high-quality WGS data and comprehensive methods, we identified the landscape of driver gene events and druggable targets in glioblastoma patients.

Targeting gene fusions in glioma

PURPOSE OF REVIEW

Glioma represents of variety of brain malignancies, the majority of which confer a poor prognosis despite treatment. With the widespread use of next-generation sequencing, gene fusions are being found in greater numbers. Gene fusions in glioma represent an opportunity to deliver targeted therapies to those with limited options for treatment.

RECENT FINDINGS

Extensive studies on these gene fusions have shown that they can exhibit distinct phenotypes, such as PTPRZ1-MET fusions in secondary glioblastoma or FGFR3-TACC3 fusions in IDH wildtype gliomas. Responses have been observed with the use of targeted therapies but some have been short lived because of the development of treatment resistance.

SUMMARY

Increasing detection of gene fusions in glioma along with basket trials have helped define different fusion phenotypes and paved the way for targeted kinase inhibitor-based therapies. Targeting NTRK fusions has been the most successful fusion-guided therapy to date and evaluating all patients for these fusions may be warranted.

t(4;12)(q12;p13) ETV6-rearranged AML without eosinophilia does not involve PDGFRA: relevance for imatinib insensitivity

Apparent ETV6-PDGFRA fusions identified by FISH analysis in t(4;12)(q12;p13) AML should be confirmed by sequencing.

Sequence-confirmed ETV6-PDGFRA fusions have not been identified in patients with t(4;12)(q12;p13) AML without eosinophilia.

Acute myeloid leukemia (AML) with t(4;12)(q12;p13) translocation is rare and often associated with an aggressive clinical course and poor prognosis. Previous reports based on fluorescence in situ hybridization (FISH) analysis have suggested that ETV6::PDGFRA fusions are present in these patients, despite the absence of eosinophilia, which is typically found in other hematopoietic malignancies with PDGFRA-containing fusions. We first detected an ETV6-SCFD2 fusion by targeted RNA sequencing in a patient with t(4;12)(q12;p13) who had been diagnosed with an ETV6-PDGFRA fusion by FISH analysis but failed to respond to imatinib. We then retrospectively identified 4 additional patients with AML and t(4;12)(q12;p13) with apparent ETV6-PDGFRA fusions using chromosome and FISH analysis and applied targeted RNA sequencing to archival material. We again detected rearrangements between ETV6 and non-PDGFRA 4q12 genes, including SCFD2, CHIC2, and GSX2. None of the 3 patients who received imatinib based on the incorrect assumption of an ETV6-PDGFRA fusion responded. Our findings highlight the importance of using a sequencing-based assay to confirm the presence of targetable gene fusions, particularly in genomic regions, such as 4q12, with many clinically relevant genes that are too close to resolve by chromosome or FISH analysis. Finally, combining our data and review of the literature, we show that sequence-confirmed ETV6-PDGFRA fusions are typically found in eosinophilic disorders (3/3 cases), and patients with t(4;12)(q12;p13) without eosinophilia are found to have other 4q12 partners on sequencing (17/17 cases).

Detection of NTRK fusions in glioblastoma: fluorescent in situ hybridisation is more useful than pan-TRK immunohistochemistry as a screening tool prior to RNA sequencing

Glioblastomas are frequent malignant brain tumours with a very poor prognosis and a need for new and efficient therapeutic strategies. With the approval of anti-TRK targeted therapies to treat patients with advanced NTRK-rearranged cancers, independent of the type of cancer, potential new treatment opportunities are available for the 0.5-5% of patients with NTRK-rearranged glioblastomas. Identification of these rare NTRK-rearranged glioblastomas requires efficient diagnostic tools and strategies which are evaluated in this study. We compared the results of NTRK1, NTRK2 and NTRK3 fluorescent in situ hybridisation (FISH) assays to those of pan-TRK immunohistochemistry (IHC) using two EPR17341 and A7H6R clones in a set of 196 patients with glioblastomas. Cases with at least 15% of positive nuclei using FISH analyses were further analysed using RNA sequencing. Above the 15% threshold, seven positive glioblastomas (3.57%) were identified by FISH assays (4 NTRK1, 3 NTRK2, no NTRK3). NTRK rearrangements were confirmed by RNA sequencing analyses in four cases [1 LMNA-NTRK1, 1 PRKAR2A-NTRK2, 1 SPECC1L-NTRK2 and 1 NACC2-NTRK2 fusions, i.e., 4/196 (2%) of NTRK-rearranged tumours in our series] but no rearrangement was detected in three samples with less than 30% of positive tumour nuclei as determined by NTRK1 FISH. Pan-TRK immunostaining showed major discrepancies when using either the EPR17341 or the A7H6R clones for the following criteria: main intensity, H-Score based scoring and homogeneity/heterogeneity of staining (Kappa values <0.2). This led to defining adequate criteria to identify NTRK-rearranged gliomas exhibiting strong and diffuse immunostaining contrasting to the variable and heterogeneous staining in non-NTRK-rearranged gliomas (p<0.0001). As assessing NTRK rearrangements has become crucial for glioma therapy, FISH seems to be a valuable tool to maximise access to TRK testing in patients with glioblastomas. In contrast to other cancers, pan-TRK IHC appears of limited interest in this field because there is no 'on/off' IHC positivity criterion to distinguish between NTRK-rearranged and non-NTRK-rearranged gliomas. RNA sequencing analyses are necessary in FISH positive cases with less than 30% positive nuclei, to avoid false positivity when scoring is close to the detection threshold.

Morphologic and Molecular Aspects of Glioblastomas

The definition of glioblastomas has continually evolved from a reliance on strict morphologic features to a combination of histologic and molecular criteria, as the understanding of the genetic basis of these tumors expands. Modern pathologic workup of glioblastomas includes intraoperative evaluations with tissue-sparing techniques, histologic assessment with immunohistochemical markers, and comprehensive molecular characterization aiming at personalized targeting of genetic abnormalities. Machine learning analysis of DNA methylation profiles is a breakthrough technology that has bolstered central nervous system tumor classification and discovery and is particularly beneficial for the diagnosis and subtyping of glioblastomas.

NTRK Fusions and TRK Inhibitors: Potential Targeted Therapies for Adult Glioblastoma

Introduction

Glioblastoma multiforme (GBM) is the most common primary central nervous (CNS) system malignancy with a poor prognosis. The standard treatment for GBM is neurosurgical resection, followed by radiochemotherapy and adjuvant temozolomide chemotherapy. Predictive biomarkers, such as methylation of the promoter region of the O6-methylguanine DNA methyltransferase (MGMT) gene, can successfully distinguish subgroups with different prognosis after temozolomide chemotherapy. Based on multiomics studies, epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF), BRAF V600E mutation, neurotrophic tyrosine receptor kinase (NTRK) fusions and other potential therapy targets have been found.

Methods

We have reviewed the preclinical and clinical evidence for NTRK fusions and TRK inhibitors therapy in cancers with NTRK fusions in pan-cancer and gliomas.

Results

Several NTRK1/2/3 fusions have been reported in GBM and preclinical studies have proven that NTRK fusions are potential driver mutations in some high-grade gliomas. Tropomyosin receptor kinase (TRK) inhibitors have shown efficacy as targeted therapies for extracranial tumors with NTRK fusions in recent clinical trials, with potential CNS tolerability and activity. However, whether NTRK gene fusions can affect survival status, the efficacy and resistance of TRK inhibitors in GBMs are lacking high-level evidences.

Conclusions

For GBM patients, NTRK fusions and TRK inhibitors are potential target therapy strategy but remain biological mechanism and clinical significance unclarified. More clinical data and future clinical trials are needed to provide more evidence that supports targeted therapy for GBM with NTRK fusions.