Atypical teratoid rhabdoid tumor: molecular insights and translation to novel therapeutics

RRM2 inhibition alters cell cycle through ATM/Rb/E2F1 pathway in atypical teratoid rhabdoid tumor

BACKGROUND

Atypical teratoid rhabdoid tumor (ATRT) is an aggressive brain tumor that mainly affects young children. Our recent study reported a promising therapeutic strategy to trigger DNA damage, impede homologous recombination repair, and induce apoptosis in ATRT cells by targeting ribonucleotide reductase regulatory subunit M2 (RRM2). COH29, an inhibitor of RRM2, effectively reduced tumor growth and prolonged survival in vivo. Herein, we explored the underlying mechanisms controlling these functions to improve the clinical applicability of COH29 in ATRT.

METHODS

Molecular profiling of ATRT patients and COH29-treated cells was analyzed to identify the specific signaling pathways, followed by validation using a knockdown system, flow cytometry, q-PCR, and western blot.

RESULTS

Elevated E2F1 and its signaling pathway were correlated with poor prognosis. RRM2 inhibition induced DNA damage and activated ATM, which reduced Rb phosphorylation to promote Rb-E2F1 interaction and hindered E2F1 functions. E2F1 activity suppression led to decreased E2F1-dependent target expressions, causing cell cycle arrest in the G1 phase, decreased S phase cells, and blocked DNA damage repair.

CONCLUSION

Our study highlights the role of ATM/Rb/E2F1 pathway in controlling cell cycle arrest and apoptosis in response to RRM2 inhibition-induced DNA damage. This provides insight into the therapeutic benefits of COH29 and suggests targeting this pathway as a potential treatment for ATRT.

Absence of SMARCB1 in rhabdoid tumor cells increases sensitivity to translation inhibition and alters translation efficiency of specific mRNAs

Rhabdoid tumors, characterized and driven by the loss of the mammalian SWItch/sucrose nonfermentable subunit SMARCB1, are very aggressive childhood cancers that can arise in the brain, the kidney, or soft tissues. Cell lines derived from these tumors are specifically sensitivity to the translation inhibitor homoharringtonine. Having recently demonstrated mammalian SWItch/sucrose nonfermentable roles in translation, we assessed SMARCB1 potential roles in translation in rhabdoid tumor cells. We first revealed by cell viability assays that rhabdoid tumor cells' sensitivity to homoharringtonine were dependent on the absence of SMARCB1. Polysome profiling and immunoprecipitation experiments demonstrated the interaction of SMARCB1 with translation machinery. Global translation assays and ribosome profiling experiments further revealed that SMARCB1 re-expression increased global translation and altered translation efficiency of specific mRNAs. Most regulated mRNAs presented an increased translation efficiency and were involved in differentiation. In comparison with the entire transcriptome, these mRNAs presented a longer coding sequence and were enriched in GC. Finally, we demonstrated that SMARCB1 re-expression increased cytoplasmic localization of these mRNAs and that gene encoding these transcripts were bound by SMARCA4 and SMARCC1. In conclusion, this study reveals that the loss of SMARCB1 in rhabdoid tumors has specific consequences on mRNAs translation with potential to unveil new dependencies.

Pediatric skull base tumors: Clinical features and surgical outcomes; a single center retrospective study with a review of literature

Objectives

Pediatric intracranial tumors, particularly at the skull base, are rare and present unique challenges to pediatric neurosurgeons and oncologists, owing to their complex anatomy and diverse histopathology. Robust evidence is still marginal concerning their clinical and surgical courses. Our aim is to describe our experience regarding surgical approaches, with special focus on surgical features, postoperative outcomes, adverse events as well as adjuvant therapeutic concepts.

Methods

Patients aged <18 years undergoing skull base surgery between 2017 and 2023 at our institution were retrospectively enrolled. Patient demographics, tumor characteristics, surgical approach, pre -and postoperative clinical status and adjuvant therapy as well as overall and progression free survival were assessed.

Results

Twelve children aged 6.1 ± 4.1 years were analyzed. There was a predominance of the female gender (7/12, 58.4%). Mean tumor diameter was 4.0 ± 2.9 cm. In three children the tumor was located suprasellar, temporobasal in one, adjacent to the cerebellar pontine angle in 4, clival in 3 and petroclival in 2 children. A subfrontal approach was performed in two patients, a subtemporal approach in one, a retrosigmoidal approach in 5 and in one patient two-staged approach; retrosigmoidal and later in a second operation pterional approach was conducted. One clival tumor was removed via an endonasal endoscopic approach and in another case via a transoral endoscopic approach. Gross total resection (GTR) and near total resection were achieved in 7 patients (58.3%). Tumor types included meningioma, clivus-chordoma, epidermoid cyst, anaplastic ependymoma, Ewing's sarcoma and Atypical Teratoid Rhabdoid Tumor (ATRT) as well as embryonal tumor with multilayered rosettes (ETMR). 4 patients (33.3%) died of disease due to tumor progression in average after 15 months. Hydrocephalus developed in two patients; a ventriculoperitoneal shunt was inserted in one patient, while an endoscopic third ventriculostomy (ETV) was performed in the other. Moreover, one child suffered from a residual neurological deficit at last follow-up evaluation. Adjuvant therapy protocols were applied in six patients (50.0%).

Conclusion

Skull base tumors in children present a therapeutic challenge due to their rarity and unique pathological composition and can lead to considerable morbidity and mortality. An interdisciplinary approach involving neurosurgeons, pediatric oncologists and radiotherapists is mandatory to guarantee the best clinical course.

Pediatric atypical teratoid/rhabdoid tumor in the cauda equina with rapid tumor progression: illustrative case

BACKGROUND

Atypical teratoid/rhabdoid tumor (AT/RT) is an uncommon malignant neoplasm and rarely occurs in the spinal space, especially in the cauda equina. Only 8 cases of pediatric AT/RT of the cauda equina have been reported. Therefore, its clinical behavior and optimal treatment remain unclear.

OBSERVATIONS

The authors describe the case of a 9-year-old boy who presented with progressive back and left leg pain. Initial magnetic resonance imaging showed an intradural extramedullary lesion at the L3-4 level, which progressed rapidly to the L2-5 level within a month. He underwent partial resection of the tumor with an L2-5 laminectomy. The histopathological diagnosis was AT/RT. He received adjuvant chemotherapy and radiotherapy, and his gait disturbance improved postoperatively. At 6 months' follow-up, disease recurrence was not observed.

LESSONS

Although extremely rare, AT/RT should be included in the differential diagnosis for prompt therapeutic intervention. Safe resection with minimal functional impairment, followed by postoperative chemoradiation, can lead to tumor control and improve neurological function. https://thejns.org/doi/10.3171/CASE24219.

Spinal Atypical Teratoid Rhabdoid Tumor in a 14-Year-old Child With Down Syndrome: A Case Report

Individuals with 21 trisomy or Down syndrome (DS) are known to have an increased risk of acute leukemia, while they rarely develop solid or central nervous system (CNS) tumors. Atypical teratoid rhabdoid tumor (ATRT) is a highly aggressive CNS-WHO grade 4 neoplasm, which has never been reported in association with Down syndrome. We present a case study of a 14-year-old female with Down syndrome, diagnosed with intradural-extramedullary spinal ATRT. The chief complaints included bilateral lower limb weakness, constipation, and urinary incontinence for 2 weeks. Surgery was scheduled, and a biopsy was taken. The histopathology, immunohistochemistry, and molecular analysis confirmed the diagnosis of the ATRT-MYC/group 2B subgroup. This report highlights the challenges of managing a patient with complex medical conditions. Moreover, it adds to the existing literature on CNS tumors in patients with Down syndrome.

Feeder-free differentiation of human iPSCs into natural killer cells with cytotoxic potential against malignant brain rhabdoid tumor cells

Natural killer (NK) cells are cytotoxic immune cells that can eliminate target cells without prior stimulation. Human induced pluripotent stem cells (iPSCs) provide a robust source of NK cells for safe and effective cell-based immunotherapy against aggressive cancers. In this in vitro study, a feeder-free iPSC differentiation was performed to obtain iPSC-NK cells, and distinct maturational stages of iPSC-NK were characterized. Mature cells of CD56bright CD16bright phenotype showed upregulation of CD56, CD16, and NK cell activation markers NKG2D and NKp46 upon IL-15 exposure, while exposure to aggressive atypical teratoid/rhabdoid tumor (ATRT) cell lines enhanced NKG2D and NKp46 expression. Malignant cell exposure also increased CD107a degranulation markers and stimulated IFN-γ secretion in activated NK cells. CD56bright CD16bright iPSC-NK cells showed a ratio-dependent killing of ATRT cells, and the percentage lysis of CHLA-05-ATRT was higher than that of CHLA-02-ATRT. The iPSC-NK cells were also cytotoxic against other brain, kidney, and lung cancer cell lines. Further NK maturation yielded CD56-ve CD16bright cells, which lacked activation markers even after exposure to interleukins or ATRT cells - indicating diminished cytotoxicity. Generation and characterization of different NK phenotypes from iPSCs, coupled with their promising anti-tumor activity against ATRT in vitro, offer valuable insights into potential immunotherapeutic strategies for brain tumors.

Atypical teratoid rhabdoid tumor in a lower middle‑income country: Challenges to cure

Atypical teratoid rhabdoid tumor (ATRT) is a rare type of potentially fatal childhood brain tumor. The present study aimed to examine the overall survival (OS) and event-free survival (EFS) outcomes of pediatric patients with ATRT and to analyze the impact of different prognostic factors, including age, sex, tumor site and size, metastatic disease, the extent of resection, radiotherapy, and chemotherapy, on survival. The present study included 47 patients with ATRT treated at the Children's Cancer Hospital of Egypt (Cairo, Egypt) between July 2007 and December 2017. These patients were treated according to the Dana-Farber Cancer Institute protocol 02-294 for 51 weeks. Various prognostic factors, including age, sex, tumor size and initial metastatic status, exhibited no impact on the radiological response measured at 6 weeks and at the end of treatment. The primary tumor site significantly affected the response to treatment at 6 weeks (P=0.008). Toxicity-related mortality occurred in 29.8% of patients. The median duration of the treatment protocol was 66.9 weeks. The duration of treatment was in the present cohort was longer than the actual 51 weeks of the protocol due to prolonged supportive care of the included patients. Patients who encountered toxicity received reduced dose of chemotherapy in the subsequent cycles in the protocol. Age, initial metastatic status, tumor site and resection extent did not significantly affect the patient outcomes. Preoperative tumor size significantly affected the EFS (P=0.03) and OS (P=0.04). Radiotherapy administration significantly affected the OS (P<0.001) and EFS (P<0.001). The median EFS and OS of patients were 9.3 and 10.3 months, respectively. A total of 24 (51.1%) patients exhibited disease progression or recurrence. The progression sites were local (n=6), metastatic (n=9) or both local and metastatic (n=9). The results of the present study demonstrated that the therapeutic regimen should be patient-adjusted to maintain the treatment intensity and avoid toxicity-related mortality. In lower middle-income countries, short and intensified induction followed by consolidation of treatment, either by single or tandem autologous stem cell transplant, is needed to avoid prolonged exposure to myelosuppression and toxicity-related mortality.

Targeting cholesterol biosynthesis for AT/RT: comprehensive expression analysis and validation in newly established AT/RT cell line

Atypical teratoid/rhabdoid (AT/RT) is a rare and highly malignant tumor of the central nervous system (CNS). It is most commonly found in children less than 5 years of age and is associated with inactivation of loss of function of SMARCB1/INI1. An experimental model for AT/RT is necessary to develop new and effective therapies. We established a patient-derived new cell line (MZ611ATRT), which showed loss of BAF-47. MZ611ATRT genetically features somatic heterozygous deletion of SMARCB1 and single nucleotide deletion of the residual allele, exon 5 ([c.541delC]), resulting in a stop codon at codon 954 by frameshift. We assessed the RNA-sequencing data of the other two AT/RT cell lines with forced expression of SMARCB1 available from public databases. We found SMARCB1 overexpression significantly down-regulates the expression of a group of enzymes related to cholesterol biosynthesis. Simvastatin was highly sensitive against MZ611ATRT cells and induced apoptosis (IC50 was 3.098 µM for MZ611ATRT, 41.88uM for U-87 MG, 23.34uM for IOMM-Lee, and 18.12uM for U-251 MG.). Pathways involved in cholesterol biosynthesis may be new targets for adjuvant therapy of AT/RT.

Primary orbital rhabdoid tumour masquerading as atypical persistent foetal vasculature

We present a case of primary rhabdoid tumour of the orbit. Presenting features at birth included congenital ptosis, conjunctival injection, hyphaema and microphthalmia. The unique presentation caused a late diagnosis following the development of rapid proptosis 6 months later. We suggest that orbital rhabdoid tumour be considered in the differential diagnoses of patients presenting with atypical persistent foetal vasculature features.

Development and epigenetic regulation of Atypical teratoid/rhabdoid tumors in the context of cell-of-origin and halted cell differentiation

Atypical teratoid/rhabdoid tumors (AT/RTs) are aggressive brain tumors primarily observed in infants. The only characteristic, recurrent genetic aberration of AT/RTs is biallelic inactivation of SMARCB1 (or SMARCA4). These genes are members of the mSWI/SNF chromatin-remodeling complex, which regulates various developmental processes, including neural differentiation. This review explores AT/RT subgroups regarding their distinct SMARCB1 loss-of-function mechanisms, molecular features, and patient characteristics. Additionally, it addresses the ongoing debate about the oncogenic relevance of cell-of-origin, examining the influence of developmental stage and lineage commitment of the seeding cell on tumor malignancy and other characteristics. Epigenetic dysregulation, particularly through the regulation of histone modifications and DNA hypermethylation, has been shown to play an integral role in AT/RTs' malignancy and differentiation blockage, maintaining cells in a poorly differentiated state via the insufficient activation of differentiation-related genes. Here, the differentiation blockage and its contribution to malignancy are also explored in a cellular context. Understanding these mechanisms and AT/RT heterogeneity is crucial for therapeutic improvements against AT/RTs.

Targeting of RRM2 suppresses DNA damage response and activates apoptosis in atypical teratoid rhabdoid tumor

BACKGROUND

Atypical teratoid rhabdoid tumors (ATRT) is a rare but aggressive malignancy in the central nervous system, predominantly occurring in early childhood. Despite aggressive treatment, the prognosis of ATRT patients remains poor. RRM2, a subunit of ribonucleotide reductase, has been reported as a biomarker for aggressiveness and poor prognostic conditions in several cancers. However, little is known about the role of RRM2 in ATRT. Uncovering the role of RRM2 in ATRT will further promote the development of feasible strategies and effective drugs to treat ATRT.

METHODS

Expression of RRM2 was evaluated by molecular profiling analysis and was confirmed by IHC in both ATRT patients and PDX tissues. Follow-up in vitro studies used shRNA knockdown RRM2 in three different ATRT cells to elucidate the oncogenic role of RRM2. The efficacy of COH29, an RRM2 inhibitor, was assessed in vitro and in vivo. Western blot and RNA-sequencing were used to determine the mechanisms of RRM2 transcriptional activation in ATRT.

RESULTS

RRM2 was found to be significantly overexpressed in multiple independent ATRT clinical cohorts through comprehensive bioinformatics and clinical data analysis in this study. The expression level of RRM2 was strongly correlated with poor survival rates in patients. In addition, we employed shRNAs to silence RRM2, which led to significantly decrease in ATRT colony formation, cell proliferation, and migration. In vitro experiments showed that treatment with COH29 resulted in similar but more pronounced inhibitory effect. Therefore, ATRT orthotopic mouse model was utilized to validate this finding, and COH29 treatment showed significant tumor growth suppression and prolong overall survival. Moreover, we provide evidence that COH29 treatment led to genomic instability, suppressed homologous recombinant DNA damage repair, and subsequently induced ATRT cell death through apoptosis in ATRT cells.

CONCLUSIONS

Collectively, our study uncovers the oncogenic functions of RRM2 in ATRT cell lines, and highlights the therapeutic potential of targeting RRM2 in ATRT. The promising effect of COH29 on ATRT suggests its potential suitability for clinical trials as a novel therapeutic approach for ATRT.

Current Molecular and Clinical Landscape of ATRT - The Link to Future Therapies

ATRT is a highly aggressive and rare pediatric CNS tumor of very young children. Its genetic hallmark is bi-allelic inactivation of SMARCB1 encoding INI1. Rarely SMARCA4 encoding BRG1 is affected. Up to 30% are associated with constitutional heterozygous pathogenic variants in one of the two genes, giving rise to the Rhabdoid-Tumor-Predisposition-Syndromes (RTPS) 1 and 2. Characteristic DNA methylation profiles distinguish ATRT from other SMARCB1-deficient entities. Three distinct subtypes ATRT-MYC, -TYR, and -SHH are on record. ATRT-SHH may be further divided into the subgroups ATRT-SHH1A, -SHH1B, and -SHH2. The cure of ATRT remains challenging, notwithstanding an increasing understanding of molecular pathomechanisms and genetic background. The implementation of multimodal institutional treatment protocols has improved prognosis. Regardless of treatment approaches, clinical risk factors such as age, metastases, and DNA methylation subtype affect survival probability. We provide a critical appraisal of current conventional multimodal regimens and emerging targeted treatment approaches investigated in clinical trials and entity-specific registries. Intense treatment approaches featuring radiotherapy (RT) and high-dose chemotherapy (HDCT) face the difficulty of balancing tumor control and treatment-related toxicity. Current approaches focus on minimizing radiation fields by proton beam therapy or to withhold RT in HDCT-only approaches. Still, a 40-75% relapse rate upon first-line treatment reveals the need for novel treatment strategies in primary and even more in recurrent/refractory (r/r) disease. Among targeted treatments, immune checkpoint inhibitors and epigenetically active agents appear most promising. Success remains limited in single agent approaches. We hypothesize that mechanism-informed combination therapy will enhance response, as the low mutational burden of ATRT may contribute to acquiring resistance to single targeted agents. As DNA methylation group-specific gene expression profiles appear to influence response to distinct agents, the future treatment of ATRT should respect clinical and biological heterogeneity in risk group adjusted treatment protocols.

Tazemetostat in the therapy of pediatric INI1-negative malignant rhabdoid tumors

Rhabdoid tumors are aggressive tumors that may arise in the kidney, soft tissue, central nervous system, or other organs. They are defined by SMARCB1 (INI1) or SMARCA4 alterations. Often, very young children are affected, and the prognosis is dismal. Four patients with primary atypical teratoid rhabdoid tumor (AT/RT, a rhabdoid tumor in the central nervous system) were treated by resection and high dose chemotherapy. Tazemetostat was introduced after completion of chemotherapy. Three patients have achieved an event free survival of 32, 34, and 30 months respectively. One progressed and died. His overall survival was 20 months. One patient was treated for a relapsed atypical teratoid rhabdoid tumor. The treatment combined metronomic therapy, radiotherapy, tazemetostat and immunotherapy. This patient died of disease progression, with an overall survival of 37 months. One patient was treated for a rhabdoid tumor of the ovary. Tazemetostat was given as maintenance after resection, chemotherapy, and radiotherapy, concomitantly with immunotherapy. Her event free survival is 44 months. Only approximately 40% of patients with rhabdoid tumors achieve long-term survival. Nearly all relapses occur within two years from diagnosis. The event free survival of four of the six patients in our cohort has exceeded this timepoint. Tazemetostat has been mostly tested as a single agent in the relapsed setting. We present promising results when applied as maintenance or add on in the first line treatment.

Atypical Teratoid/Rhabdoid Tumor of the Nervous System in Adults: Location-Related Features and Outcome

BACKGROUND

Atypical teratoid/rhabdoid tumor (AT/RT) of the nervous system is a rare and highly malignant neoplasm, mainly affecting children, first recognized as a pathologic entity in 1996 and added to the World Health Organization Classification of the Tumors of the Central Nervous System in 2000. AT/RT is even rarer among adults and is associated with a worse prognosis. The aim of the present study was to analyze the different tumor features according to the location in adults.

METHODS

A comprehensive and detailed literature review of AT/RTs in adults was made. The demographic, management, and outcome data associated with tumor location were analyzed and compared; histopathologic and molecular features were also discussed. Furthermore, we added our personal case with brain hemispheric localization and reported a progression-free survival of 103 months after gross total resection and adjuvant radiotherapy showing a peculiar histopathologic pattern.

RESULTS

Female sex is mainly affected by AT/RT on median localizations, both intracranial and spinal, and by all sellar region cases. Gross total resection is mainly achieved among lateral compared with median localizations. Combined radiotherapy and chemotherapy is the most adopted adjuvant treatment in all tumor localizations and is related to better outcome. Postoperative death is reported only among sellar region localizations, whereas brain hemispheric cases show the best overall survival.

CONCLUSIONS

AT/RTs show different and peculiar features according to their location, which significantly affects the outcome; precise knowledge of them helps the neurosurgeon in planning the best strategy for treatment.

Health-Related Quality of Life and Mental Health of Children with Embryonal Abdominal Tumors

(1) Background: Embryonal abdominal tumors are one of the most common entities of solid childhood cancer. The present study investigates the Health-Related Quality of Life (HRQoL) and the mental health of children to obtain a comprehensive picture of their health status and uncover a possible gap in healthcare. (2) Methods: The sample consisted of 54 children who were treated for embryonal abdominal tumors and a control group of 46 children who received uncomplicated outpatient surgery. The HRQoL and the mental health were assessed by the parent proxy reports of the questionnaires Pediatric Quality of Life Inventory (PedsQL) and Strengths and Difficulties Questionnaire (SDQ). (3) Results: Children with embryonal abdominal tumors showed significantly lower HRQoL and mental health values compared to the norm data. The index group showed lower values in the social subscales of HRQoL and mental health compared to the control group. (4) Conclusions: Embryonal abdominal tumors affect the well-being of children. There is still a gap in healthcare due to children's HRQoL and mental health, especially regarding social development. It is essential to further advance the psychological care of children and improve their chances to develop social relationships.

Clinical diagnostic and radiographic features of primary spinal atypical teratoid rhabdoid tumors tumor in a pediatric patient: A case report and review of the literature

Atypical teratoid rhabdoid tumors (ATRTs) are rare embryonal tumors comprising 1-2% of all pediatric CNS neoplasms. Spinal ATRTs are even more uncommon, accounting for 2% of all reported ATRT cases. Despite their rarity, ATRTs affect young children disproportionately and are characterized by a high malignant potential due to a heterogeneous cellular composition and inactivating mutations in the SMARCB1 (90%) and SMARCA4 (10%) genes. A 15-month-old female presented with a 2-week history of decreased lower extremity movement and new-onset need for assistance with ambulation. MRI lumbar spine revealed a contrast-enhancing intradural mass at the L3-L4 level with iso-intensity on T1 and T2 sequences. The patient subsequently underwent subtotal tumor resection (∼80%) given concerns for maintaining neurological function. Final pathology was consistent with spinal ATRT, and she later underwent adjuvant chemoradiation therapy per ACNS0333 protocol. She has since remained in remission with age-appropriate developmental milestones over the past 2 years. ATRTs should be considered in the differential diagnosis of intradural spinal lesions, especially in the pediatric patient population. Clinical course, presentation, and diagnosis is often delayed due to the rarity of these tumors, but contrasted craniospinal MRI is key for diagnosis and histopathology with IHC staining showing loss of INI is confirmatory. While gross total resection is the goal, maximal safe tumor resection should be prioritized in order to preserve neurological function. Adjuvant chemoradiation following gross total/subtotal resection has been shown to significantly improve overall survival.

A Carboxy-terminal Smarcb1 Point Mutation Induces Hydrocephalus Formation and Affects AP-1 and Neuronal Signalling Pathways in Mice

The BAF (BRG1/BRM-associated factor) chromatin remodelling complex is essential for the regulation of DNA accessibility and gene expression during neuronal differentiation. Mutations of its core subunit SMARCB1 result in a broad spectrum of pathologies, including aggressive rhabdoid tumours or neurodevelopmental disorders. Other mouse models have addressed the influence of a homo- or heterozygous loss of Smarcb1, yet the impact of specific non-truncating mutations remains poorly understood. Here, we have established a new mouse model for the carboxy-terminal Smarcb1 c.1148del point mutation, which leads to the synthesis of elongated SMARCB1 proteins. We have investigated its impact on brain development in mice using magnetic resonance imaging, histology, and single-cell RNA sequencing. During adolescence, Smarcb11148del/1148del mice demonstrated rather slow weight gain and frequently developed hydrocephalus including enlarged lateral ventricles. In embryonic and neonatal stages, mutant brains did not differ anatomically and histologically from wild-type controls. Single-cell RNA sequencing of brains from newborn mutant mice revealed that a complete brain including all cell types of a physiologic mouse brain is formed despite the SMARCB1 mutation. However, neuronal signalling appeared disturbed in newborn mice, since genes of the AP-1 transcription factor family and neurite outgrowth-related transcripts were downregulated. These findings support the important role of SMARCB1 in neurodevelopment and extend the knowledge of different Smarcb1 mutations and their associated phenotypes.

Children's Oncology Group's 2023 blueprint for research: Central nervous system tumors

Tumors of the central nervous system (CNS) are a leading cause of morbidity and mortality in the pediatric population. Molecular characterization in the last decade has redefined CNS tumor diagnoses and risk stratification; confirmed the unique biology of pediatric tumors as distinct entities from tumors that occur in adulthood; and led to the first novel targeted therapies receiving Food and Drug Administration (FDA) approval for children with CNS tumors. There remain significant challenges to overcome: children with unresectable low-grade glioma may require multiple prolonged courses of therapy affecting quality of life; children with high-grade glioma have a dismal long-term prognosis; children with medulloblastoma may suffer significant short- and long-term morbidity from multimodal cytotoxic therapy, and approaches to improve survival in ependymoma remain elusive. The Children's Oncology Group (COG) is uniquely positioned to conduct the next generation of practice-changing clinical trials through rapid prospective molecular characterization and therapy evaluation in well-defined clinical and molecular groups.

Atypical teratoid/rhabdoid tumour with CDK6 amplification in a child: a case report and literature review

Atypical teratoid/rhabdoid tumours (AT/RTs) are rare central nervous system neoplasms that frequently occur in infants and children and have a very poor prognosis. In recent years, molecular analysis of AT/RTs has shown that biallelic inactivation of SMARCB1 (INI1, SNF5, BAF47) or SMARCA4 (BRG1) frequently occurs. Here, we present a case of basal ganglia AT/RT with SMARCB1 gene deficiency and CDK6 gene amplification in a 5-year-old child. A 5-year-old boy was hospitalized due to a 1-week history of frontal and parietal headache. Magnetic resonance imaging (MRI) demonstrated a 3 cm × 2 cm × 1.5 cm heterogeneous enhanced mass located at the right basal ganglia that partially protruded into the right lateral ventricle. The lesion was successfully resected under electrophysiological monitoring and neuronavigation. The postoperative pathological examination implied an AT/RT diagnosis, with loss of SMARCB1 protein, SMARCB1 gene deficiency and CDK6 gene amplification. Unfortunately, the patient died due to respiratory and circulatory failure at 5 weeks after the operation. To date, standard regimens have not yet been established due to the lack of large-scale prospective studies for AT/RT. The p16-RB signalling pathway should be considered as a potential target for AT/RT treatment modalities. Apart from traditional regimens, targeted therapies, especially CDK4/6 inhibitors, are likely a promising therapeutic option for AT/RT treatment.

The role of chromatin remodeler SMARCA4/BRG1 in brain cancers: a potential therapeutic target

The chromatin remodeler SMARCA4/BRG1 is a key epigenetic regulator with diverse roles in coordinating the molecular programs that underlie brain tumour development. BRG1 function in brain cancer is largely specific to the tumour type and varies further between tumour subtypes, highlighting its complexity. Altered SMARCA4 expression has been linked to medulloblastoma, low-grade gliomas such as oligodendroglioma, high-grade gliomas such as glioblastoma and atypical/teratoid rhabdoid tumours. SMARCA4 mutations in brain cancer predominantly occur in the crucial catalytic ATPase domain, which is associated with tumour suppressor activity. However, SMARCA4 is opposingly seen to promote tumourigenesis in the absence of mutation and through overexpression in other brain tumours. This review explores the multifaceted interaction between SMARCA4 and various brain cancer types, highlighting its roles in tumour pathogenesis, the pathways it regulates, and the advances that have been made in understanding the functional relevance of mutations. We discuss developments made in targeting SMARCA4 and the potential to translate these to adjuvant therapies able to enhance current methods of brain cancer treatment.

The Role of Immunotherapy in the Treatment of Rare Central Nervous System Tumors

Establishing novel therapies for rare central nervous system (CNS) tumors is arduous due to challenges in conducting clinical trials in rare tumors. Immunotherapy treatment has been a rapidly developing field and has demonstrated improvements in outcomes for multiple types of solid malignancies. In rare CNS tumors, the role of immunotherapy is being explored. In this article, we review the preclinical and clinical data of various immunotherapy modalities in select rare CNS tumors, including atypical meningioma, aggressive pituitary adenoma, pituitary carcinoma, ependymoma, embryonal tumor, atypical teratoid/rhabdoid tumor, and meningeal solitary fibrous tumor. Among these tumor types, some studies have shown promise; however, ongoing clinical trials will be critical for defining and optimizing the role of immunotherapy for these patients.

Pediatric Posterior Fossa ATRT: A Case Report, New Treatment Strategies and Perspectives

Posterior fossa atypical teratoid rhabdoid tumor (ATRT) is a rare childhood tumor usually associated with a dismal prognosis. Although upfront surgical gross total resection (GTR) has classically been the first line of treatment, new multimodal treatments, including two-stage surgery, are showing promising results in terms of overall survival (OS) and complication rate. We present a case of a 9-month-old child treated with two-staged surgery and chemotherapy. When deemed risky, multimodal treatments, including staged surgeries, can be a safe alternative to reduce surgical mortality and morbidity. At 23 months old, the patient had normal global development and no major impact on quality of life. We, therefore, discuss the most recent advancements from a treatment perspective, including molecular targeting.

Posterior fossa tumors in children: An update and new concepts

Background:

Posterior fossa tumors account for approximately half of the central nervous system tumors in children. Major technological advances, mainly in the fields of molecular biology and neuroimaging, have modified their classification, leading to a more detailed description of these entities. Into the classic taxonomy, used for many years, new concepts have been incorporated at times eliminating or modifying former ones.

Methods:

A literature search was conducted in PubMed using the medical subject headings involving the five most common pediatric posterior fossa tumors: diffuse midline glioma, medulloblastoma, ependymoma, atypical teratoid/rhabdoid tumor, and pilocytic astrocytoma. Only English published articles in the past 11 years that provided technological, neuroimaging, and molecular biology insight into posterior fossa tumors in children were considered.

Results:

Substantial changes have been introduced in the nomenclature of pediatric posterior fossa tumors. Diffuse midline gliomas are named based on alterations in histone H3. Molecular rearrangements of medulloblastomas are more important in defining the prognosis than histological variants; therefore, these tumors are currently named based on their molecular subgroups. Posterior fossa ependymomas and atypical teratoid rhabdoid tumor classification have incorporated new groups based on different genetic profiles. Pilocytic astrocytoma has been placed in a new category that distinguishes circumscribed from diffuse entities.

Conclusion:

Advances in molecular biology and neuroimaging have substantially changed the way pediatric neoplasms are studied. The classical taxonomy has been modified leading to more accurate classifications that are based on the genetic alterations.

Recent progress and novel approaches to treating atypical teratoid rhabdoid tumor

Atypical teratoid rhabdoid tumors (AT/RT) are malignant central nervous system (CNS) tumors that occur mostly in young children and have historically carried a very poor prognosis. While recent clinical trial results show that this tumor is curable, outcomes are still poor compared to other central nervous system embryonal tumors. We here review prior AT/RT clinical trials and highlight promising pre-clinical results that may inform novel clinical approaches to this aggressive cancer.

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.

Molecular targeted therapies for pediatric atypical teratoid/rhabdoid tumors

Atypical teratoid/rhabdoid tumors (AT/RTs) are lethal central nervous system tumors, which are primarily diagnosed in infants. Current treatments for AT/RTs include surgery, radiotherapy, and chemotherapy; these treatments have poor prognoses and challenging side effects. The pivotal genetic event in AT/RT pathogenesis comprises the inactivation of SMARCB1 or SMARCA4. Recent epigenetic studies have demonstrated mutual and subtype-specific epigenetic derangements that drive tumorigenesis; the exploitation of these potential targets might improve the dismal treatment outcomes of AT/RTs. This review aims to summarize the literature concerning targeted molecular therapies for pediatric AT/RTs.

Atypical Teratoid/Rhabdoid Tumor in Taiwan: A Nationwide, Population-Based Study

Simple Summary

Atypical teratoid/rhabdoid tumor (AT/RT) is a rare, highly malignant CNS neoplasm with poor prognosis. A retrospective population-based analysis of patients with the diagnosis of AT/RT, registered between 1999 and 2014 in Taiwan, showed that: (1) AT/RT had a higher prevalence in males, in children < 36 months of age, and at infratentorial sites; (2) older age (≥12 months), presence of the tumor in the supratentorial region, use of radiotherapy, chemotherapy, or both were associated with better prognosis compared to surgery or no treatment. These data represent a historical experience with AT/RT in Taiwan and may inform risk stratification and clinical trial design.

Abstract

Background: Atypical teratoid/rhabdoid tumor (AT/RT) is a rare, highly aggressive embryonal brain tumor most commonly presenting in young children. Methods: We performed a nationwide, population-based study of AT/RT (ICD-O-3 code: 9508/3) in Taiwan using the Taiwan Cancer Registry Database and the National Death Certificate Database. Results: A total of 47 cases (male/female = 29:18; median age at diagnosis, 23.3 months (IQR: 12.5–87.9)) were diagnosed with AT/RT between 1999 and 2014. AT/RT had higher prevalence in males (61.70%), in children < 36 months (55.32%), and at infratentorial or spinal locations (46.81%). Survival analyses demonstrated that patients ≥ 3 years of age (n = 21 (45%)) had a 5y-OS of 41% (p < 0.0001), treatment with radiotherapy only (n = 5 (11%)) led to a 5y-OS of 60%, treatment with chemotherapy with or without radiotherapy (n = 27 (62%)) was associated with a 5y-OS of 45% (p < 0.0001), and patients with a supratentorial tumor (n = 11 (23%)) had a 5y-OS of 51.95%. Predictors of better survival on univariate Cox proportional hazard modeling and confirmed with multivariate analysis included older age (≥1 year), supratentorial sites, and the administration of radiotherapy, chemotherapy, or both. Gender had no effect on survival. Conclusion: Older age, supratentorial site, and treatment with radiotherapy, chemotherapy, or both significantly improves the survival of patients with AT/RT.

Maternal embryonal leucine zipper kinase immunoreactivity in atypical teratoid/rhabdoid tumors: a study of 50 cases

Atypical teratoid/rhabdoid tumors (AT/RTs) are aggressive embryonal neoplasms of the central nervous system that correspond to WHO grade IV and have a dismal prognosis. The latest Central Brain Tumor Registry of the United States data shows that AT/RT constitutes 16.6% of all embryonal tumors in children. The molecular hallmark of this tumor is pathogenic SMARCB1 genetic alterations resulting in the loss of INI-1 immunopositivity, with fewer tumors harboring SMARCA4 (BRG1) variants. Maternal embryonal leucine zipper kinase (MELK) is a member of the Snf1/AMPK family of serine/threonine-protein kinases involved in various processes such as cell cycle regulation, self-renewal of stem cells, apoptosis, and splicing regulation. Recent studies have highlighted the involvement of MELK in AT/RT and its possible therapeutic role. The purpose of this study was to review the histological and immunohistochemical profile of AT/RT with special reference to MELK  staining. In this retrospective study conducted over 6 years, all diagnosed cases of AT/RT, defined by loss of INI-1 immunopositivity, were retrieved and studied. Demographic details of patients and microscopic findings were analyzed, with special attention to histological patterns and immunohistochemistry profile including MELK immunoreactivity. There were 50 cases of AT/RT diagnosed in the specified period. Of the cases operated at our institute during this period, embryonal tumors constituted 20.6% of all pediatric brain tumors with AT/RT representing 12.6% of this subset. The median age at presentation was 3.5 years (range: 8 months-22 years) and there were three adult cases. Males outnumbered females by a ratio of 1.94:1. Tumor location was distributed equally between the supratentorial and infratentorial compartments. Characteristic rhabdoid cells were identified in 70% of cases. Areas with epithelial, mesenchymal, and undifferentiated tumor cells were seen in 8%, 20%, and 52% of cases, respectively. Cells with vacuolated cytoplasm were noted in 28% of cases. Immunohistochemistry (IHC) showed a polyimmunophenotypic profile with immunopositivity for GFAP in 70%, Vimentin in 100%, SMA in 68%, and EMA in 88% of cases, indicating the remarkable heterogeneity of the tumor cells. MELK immunopositivity was noted in 83.33% of cases. Thus, atypical teratoid/rhabdoid tumors are rare neoplasms. In line with other studies, we show that these tumors occur predominantly in very young children and display marked variability on histology and IHC with loss of INI-1. MELK is presumed to be an important molecule involved in cell cycle regulation, proliferation, and other critical functions. High expression of MELK in AT/RT may suggest its plausible role in neoplastic transformation of embryonic and postnatal multipotent neural progenitors which in turn could explain the diverse morphological and immunohistochemical characteristics observed in these tumors.

Utilizing preclinical models to develop targeted therapies for rare central nervous system cancers

Patients with rare central nervous system (CNS) tumors typically have a poor prognosis and limited therapeutic options. Historically, these cancers have been difficult to study due to small number of patients. Recent technological advances have identified molecular drivers of some of these rare cancers which we can now use to generate representative preclinical models of these diseases. In this review, we outline the advantages and disadvantages of different models, emphasizing the utility of various in vitro and ex vivo models for target discovery and mechanistic inquiry and multiple in vivo models for therapeutic validation. We also highlight recent literature on preclinical model generation and screening approaches for ependymomas, histone mutated high-grade gliomas, and atypical teratoid rhabdoid tumors, all of which are rare CNS cancers that have recently established genetic or epigenetic drivers. These preclinical models are critical to advancing targeted therapeutics for these rare CNS cancers that currently rely on conventional treatments.

Pediatric Neuro-Oncology

Central nervous system (CNS) tumors are the most common solid tumor in pediatrics and represent the largest cause of childhood cancer-related mortality. With advances in molecular characterization of tumors, considerable developments have occurred impacting diagnosis and management, and refined prognostication. Advances in management have led to better survival, but mortality remains high and significant morbidity persists. Novel therapeutic approaches targeting the biology of these tumors are being investigated to improve overall survival and decrease treatment-related morbidity. Further molecular understanding of pediatric CNS tumors will lead to continued refinement of tumor classification, management, and prognostication.

MiRNAs in early brain development and pediatric cancer: At the intersection between healthy and diseased embryonic development

The size and organization of the brain are determined by the activity of progenitor cells early in development. Key mechanisms regulating progenitor cell biology involve miRNAs. These small noncoding RNA molecules bind mRNAs with high specificity, controlling their abundance and expression. The role of miRNAs in brain development has been studied extensively, but their involvement at early stages remained unknown until recently. Here, recent findings showing the important role of miRNAs in the earliest phases of brain development are reviewed, and it is discussed how loss of specific miRNAs leads to pathological conditions, particularly adult and pediatric brain tumors. Let-7 miRNA downregulation and the initiation of embryonal tumors with multilayered rosettes (ETMR), a novel link recently discovered by the laboratory, are focused upon. Finally, it is discussed how miRNAs may be used for the diagnosis and therapeutic treatment of pediatric brain tumors, with the hope of improving the prognosis of these devastating diseases.