Atypical Teratoid Rhabdoid Tumor Research Articles

ATRT-17. CAR T CELL THERAPY TARGETING CLAUDIN-6 IS EFFECTIVE IN CELLULAR AND XENOGRAFT MODELS OF ATYPICAL TERATOID/RHABDOID TUMOR

Abstract Novel therapies are needed to for the treatment of atypical teratoid/rhabdoid tumor (ATRT), an aggressive brain tumor that predominantly affects young children and has an average 5-year survival under 50%. Claudin-6 (CLDN6) is a tight junction protein present during development and is expressed in up to 70% of ATRT specimens but not in normal tissue, making it a promising immunotherapeutic target. CLDN6-targeted chimeric antigen receptor (CAR) T cells in combination with a CAR T cell-amplifying mRNA vaccine have demonstrated antitumor activity against other CLDN6-expressing cancers in pre-clinical and a phase I adult trial (NCT04503278; Haanen J et al AACR, 2022). To assess the effectiveness of CLDN6-targeted CAR T cells against ATRT, we utilized a second-generation mRNA CAR with a 4-1BB costimulatory domain and single-chain variable fragment against CLDN6 (Reinhard et al, 2020). CLDN6 expression in patient-derived ATRT specimens was profiled by RNAseq (mean FPKM 11.4) and immunohistochemistry (positive staining in 53% of specimens). Tumor-derived cell lines were assessed for CLDN6 expression by flow cytometry. Co-culture of CLDN6-directed mRNA CAR T cells resulted in tumor-specific cytotoxicity compared to CD19-directed control CAR T cells in CLDN6-positive ATRT cell lines 7316-2187 (92% versus 15% at 10:1, p < 0.0001; 86% versus 0% at 5:1, p<0.0001) and 7316-2141 (75% versus 7% at 10:1, p<0.0001; 53% versus 0% at 5:1, p< 0.0001). Patient-derived, orthotopic xenograft ATRT models were created through intracranial injection of tumor cells into the cerebellum of NSG mice. Following engraftment with 7316-2141, repeated intratumoral administration of mRNA CLDN6 CAR T cells resulted in significant tumor regression (-1.9x108 vs. +2.4x109 p/sec/cm2/sr, p<0.001) and improved survival compared to mRNA CD19 CAR T cells (median OS not reached vs. 13 days, p=0.002). This work highlights the potential for targeting CLDN6 via CAR T cell therapy in patients with ATRT as a novel therapeutic strategy.

IMG-04. POTENTIAL TARGETS FOR THERANOSTICS IN PEDIATRIC HIGH-GRADE CENTRAL NERVOUS SYSTEM (CNS) TUMORS

Abstract Theranostics refers to the combination of a radioactive drug to identify (diagnose) and another radioactive drug to deliver therapy to cancer. In adult cancer several radiopharmaceuticals with specificity for receptors like cx-chemokine-receptor type 4 (CXCR-4), prostate-membrane specific antigen (PSMA), and somatostatine receptor (SSTR2a) are used. Especially PSMA for prostate cancer and SSTR2a ligands for neuro-endocrine tumors have proven their value. Moreover, novel promising targets like B7-H3 are upcoming. In children the potential of such theranostic drugs have been minimally explored. AIM of this study is to explore the expression of theranostic markers CXCR-4, PSMA, SSTR2a and B7-H3 in a broad cohort of high-grade pediatric CNS tumors to determine the potential of these imaging ligands in this cohort. METHODS The expression of CXCR-4, PSMA, SSTR2a and B7-H3 were examined both by RNA (by bulk RNAsequencing) and protein level (by immunohistochemistry (IHC)) (RNA n=161/IHC n=52) in pediatric high-grade CNS tumors: ependymomas (n=33/11), atypical teratoid rhabdoid tumors (ATRT) (n=9/7), medulloblastomas (n=51/11), diffuse midline gliomas H3K27-altered (n=27/9) and other high-grade gliomas (n=41/15). RESULTS mRNA expression of CXCR-4 was present but low in most tumor types, with the highest expression in medulloblastoma. Immunohistochemistry showed variable CXCR-4 expression, with the highest expression in some medulloblastomas, ependymomas and ATRTs. PSMA (FOLH1) mRNA and protein expression was generally very low. As expected SSTR2a showed a very high mRNA and protein expression only in medulloblastoma samples. Remarkably, B7-H3 (CD276) showed a relatively high expression in all high-grade pediatric CNS tumor types, both on RNA and protein level. CONCLUSION Of the four potential theranostic targets tested, SSTR2a is an interesting antigen in medulloblastoma. CXCR-4 could be of interest for individual patients with medulloblastoma, ATRT or ependymoma. Finally, B7-H3 is widely but variably expressed on all different tumor types, and seems a promising novel target for theranostics in pediatric CNS tumors.

OTHR-07. CIRCULATING MIRNAS AS A NON-INVASIVE MONITORING TOOL FOR PEDIATRIC BRAIN TUMORS

Abstract Current management of pediatric brain tumor patients relies on imaging as the only non-invasive tool available for monitoring therapeutic response and tumor progression. Results are often inconclusive and unable to capture biological changes that presage progression on imaging. Circulating miRNA provides an attractive non-invasive platform because miRNA’s essential role in regulating gene expression, stability in bio-fluids, selective over-expression in tumors, and subsequent active release from tumors into the extracellular environment. We aimed to establish the prognostic and monitoring value of miRNA biomarkers for pediatric brain tumors. We performed miRNA profiling of CSF (n=33) and plasma (n=53) samples across a cohort of 54 pediatric brain tumors from 6 histologies (low grade glioma, ependymoma, germ cell tumor, medulloblastoma, atypical teratoid rhabdoid tumor and high-grade glioma). We utilized unsupervised consensus clustering, differential expression, and machine learning methods to explore miRNA biomarkers. Plasma miRNA signatures were correlated with WHO Grade while CSF signatures revealed a correlation with leptomeningeal disease and higher disease burden (p<0.05). The expression of circulating miRNA revealed histology-specific signatures for low grade glioma, medulloblastoma and germinoma in plasma and CSF (p<0.05). We identified miRNA signatures of significant translational value: (1) A medulloblastoma specific miRNA in CSF can serve as a potential biomarker for tumor monitoring (medulloblastoma specificity was confirmed in independent tissue-based dataset); (2) Pilocytic astrocytoma can be distinguished from high grade glioma in CSF; (3) Most intriguingly, in plasma, miRNA expression identified pilocytic astrocytoma that had relapsed in several months after initial intervention (p<0.05). These results support circulating miRNA in plasma and CSF as biomarkers of diverse clinical diagnostic and prognostic measures. Further utilization of this approach provides unique platforms to inform liquid biopsy-based management in the clinical setting.

TRLS-15. TARGETED THERAPY IN PEDIATRIC CNS TUMORS - A SINGLE INSTITUTION EXPERIENCE

Abstract Primary central nervous system malignancy treatment remains a difficult problem despite advancement in techniques. Personalized medicine is evolving in making treatment decisions and particular molecular characteristics allow new targeted therapies to be specific and effective. We retrospectively present patients with primary CNS tumors receiving targeted therapy from 2016 to the present date. Outcomes included length of therapy, time until progression of disease, and overall response. Our study includes 32 patients with malignancies such as Astrocytoma, Ganglioglioma, Glioblastoma, and Diffuse Intrinsic Pontine Glioma (DIPG), among others. Analysis was based on patients’ underlying malignancy and included variables such as identified mutations, targeted therapy, progression vs resolution of disease, and time to progression of disease after initiation of targeted therapy. Overall results show 23 patients with at least 1-year-survival. The most common targeted therapy was Trametinib, treating tumors of glial origin. 14 patients showed no progression after starting targeted therapy, the majority low grade Gliomas and Medulloblastomas. Multiple mutations were found with the most frequent being BRAF. Of our 11 patients with BRAF mutations, 8 had no progression of disease after starting Trametinib or Dabrafenib. Patients with Atypical Teratoid Rhabdoid Tumors (ATRT) were treated with either Alisertib or Alisertib/Tazemetostat and 2 out of 4, both treated with Alisertib maintenance therapy, had no disease progression after targeted therapy. Best outcomes with no disease progression were primarily Gliomas, treated with Trametinib, and Medulloblastomas, treated with Vismodegib. Of our patients with DIPG, treated with Ribociclib, average time to disease progression on targeted therapy was 4.7 months and survival rate was 33%. We have shown excellent use of targeted therapy and our analysis highlights the need for continued exploration of targeted therapy among patients with CNS tumors.

BIOL-21. PATIENT-DERIVED, THREE-DIMENSIONAL ORGANOID PLATFORM FOR PEDIATRIC BRAIN TUMOR MODELING AND THERAPEUTIC TESTING

Abstract Brain tumors are the leading cause of cancer-related death in children. An important hurdle to scientific and clinical progress in the field has been the limited availability of preclinical tumor models. In recent years, the Children’s Brain Tumor Network (CBTN) has accelerated the development of patient-derived cell lines and xenografts, offering these resources to the community through open-source access. While these models are extremely valuable, their development process can be lengthy and result in clonally selected lines which presents a challenge for studying complex tumor biology. To address the need for three-dimensional tissue culture, our group in conjunction with CBTN, generates organoids from fresh tissue specimens obtained directly from surgical resection. This effort resulted in numerous organoid models generated for high-grade glioma (HGG), medulloblastoma, ependymoma, atypical teratoid-rhabdoid tumor, and low-grade glioma tumors. The tissue was processed within an hour post-extraction and cultured in growth factor-free media. Organoid formation and growth were observed as early as in 2 weeks post initiation and continued for up to three months. Banked organoids established growth upon return to culture and resembled similar cell composition to those in the original culture. This provides an excellent preclinical testing model for precision medicine-driven trials. To represent this, we utilized CAR-T testing approach and treated GD2-positive HGG organoids with GD2 CAR-T cells and control CD19 CAR-T cells. 72h exposure to GD2 CAR-T induced morphological changes and significant increase in dead cells within organoids, which was not observed in CD19 CAR-T treated counterparts (p<0.05). Here we provide a simple and efficient workflow for the generation and testing of three-dimensional tumor organoid models generated from fresh surgical tissue. The platform can accelerate not only tumor biology explorations but also empower a diverse array of precision medicine-driven testing for pediatric brain tumors.

Pediatric posterior fossa tumors

Tumors of the posterior fossa account for about 50-55% of brain tumors in childhood. The most frequent tumor entities are medulloblastomas, pilocytic astrocytomas, ependymomas, diffuse midline gliomas and atypical teratoid-rhabdoid tumors. Neuroradiological differential diagnosis with magnetic resonance imaging (MRI) is of considerable importance for preoperative planning as well as planning of follow-up therapy. Most important findings for differential diagnosis of pediatric posterior fossa tumors are tumor location, patient age and the intratumoral apparent diffusion assessed by diffusion-weighted imaging. Advanced MR techniques like MRI perfusion and MR spectroscopy can be helpful both in the initial differential diagnosis and in tumor surveillance, but exceptional characteristics of certain tumor entities should be kept in mind. Standard clinical MRI sequences including diffusion-weighted imaging are the main diagnostic tool in evaluating posterior fossa tumors in children. Advanced imaging methods can be helpful, but should never be interpreted separately from conventional MRI sequences.

DIPG-55. DIRECT BRAIN-TO-BRAIN WORKFLOW ENABLES THE PRECLINICAL MODELING OF PEDIATRIC GLIOMAS

Abstract Pediatric high-grade gliomas (pHGG) are one of the leading causes of brain cancer deaths in children. Progress towards the characterization of molecular and genetic features in adult high-grade gliomas and subsequent therapies has not yielded similar results in pHGG patients. pHGGs do not readily establish in culture and there has also been a lack of preclinical models to identify new therapeutic targets. Here, we employ a direct brain-to-brain workflow enabling the establishment of rare pediatric tumors including Atypical Teratoid/Rhabdoid Tumor (ATRT), H3_K27ALT diffuse midline gliomas, and H3_G34MUT diffuse hemispheric xenograft models. These Direct, Patient-Derived Orthotopic Xenografts (DPDOX) models recapitulate the clinical, genomic, and transcriptomic landscape of that of the parental tumors. Moreover, we have incorporated each tumor with a secreted gaussia luciferase reporter enabling the minimally-invasive tracking of intracranial tumor burden over time in response to drug perturbations. Taken together, we present a novel approach to establish pHGG models and evaluate new therapeutics.

Novel Strategy Involving High-Dose Chemotherapy with Stem Cell Rescue Followed by Intrathecal Topotecan Maintenance Therapy without Whole-Brain Irradiation for Atypical Teratoid/Rhabdoid Tumors

Atypical teratoid/rhabdoid tumor (AT/RT) is a rare aggressive central nervous system tumor that typically affects children under three years old and has poor survival with a high risk for neurologic deficits. The primary purpose of this study was to successfully treat the disease and delay or avoid whole-brain radiotherapy for children with AT/RT. A retrospective analysis was performed for six children diagnosed with AT/RT and treated with multimodal treatment at a single institute between 2014 and 2020. Furthermore, germline SMARCB1 aberrations and MGMT methylation status of the tumors were analyzed. One patient who did not receive a modified IRS-III regimen replaced with ifosphamide, carboplatin, and etoposide (ICE) in induction chemotherapy was excluded from this analysis. Five patients who received ICE therapy were under three years old. After a surgical approach, they received intensive chemotherapy and high-dose chemotherapy with autologous peripheral blood stem cell transplantation (HDCT/autoPBSCT) followed by intrathecal topotecan maintenance therapy. Three patients underwent single HDCT/autoPBSCT, and the other two received sequential treatment. Two patients with germline SMARCB1 aberrations and metastases died of progressive AT/RT or therapy-related malignancy, while 3 with localized tumors without germline SMARCB1 aberrations remained alive. One survivor received local radiotherapy only, while the other two did not undergo radiotherapy. All three surviving patients were able to avoid whole-brain radiotherapy. Our results suggest that AT/RT patients with localized tumors without germline SMARCB1 aberrations can be rescued with multimodal therapy, including induction therapy containing ICE followed by HDCT/autoPBSCT and intrathecal topotecan maintenance therapy without radiotherapy. Further large-scale studies are necessary to confirm this hypothesis.

Phase 1/2 study of tiragolumab and atezolizumab in patients with relapsed or refractory SMARCB1 or SMARCA4 deficient tumors.

TPS10066 Background: The SMARCB1/A4 gene products are core subunits of the SWItch/Sucrose Non-fermentable (SWI/SNF) chromatin remodeling complex. Tumors with defects in SWI/SNF are histologically distinct aggressive cancers occurring in children and young adults. SMARCB1/A4 deficient tumors, particularly rhabdoid tumors, poorly differentiated chordoma, epithelioid sarcoma, and medullary renal cell carcinoma, have immune cell infiltrates and programmed death ligand 1 (PD-L1) expression. Response to immune checkpoint inhibition (CI) has been observed in SMARCB1/A4 deficient tumors; however, responses are not durable. T cell immunoreceptor with Ig and ITIM domains (TIGIT) is a novel inhibitory receptor expressed on multiple immune cells. TIGIT inhibits T and NK cells by binding to its ligand poliovirus receptor (PVR) and Nectin2 on tumor cells and antigen-presenting cells. Utilizing RNAseq data, SMARCB1/A4 deficient tumors demonstrate high expression of PVR and Nectin2. Tiragolumab is an antibody to the TIGIT receptor. In patients with non-small cell lung cancer, tiragolumab with atezolizumab increased survival compared to atezolizumab alone. Thus, data suggest that SMARCB1/A4 deficient tumors are susceptible to CI; however, monotherapy is unlikely to achieve durable responses; the addition of tiragolumab may enhance response rates. Methods: This is a phase 1/2 trial of tiragolumab monotherapy and in combination with atezolizumab in patients ≥ 12 months of age with SMARCB1/A4 deficient tumors administered IV on Day 1 of 21-day cycles. Part A will evaluate the safety of tiragolumab monotherapy (300 mg if ≤ 15 kg; 420 mg if >15 to ≤ 40 kg; 600 mg if > 40 kg or ≥ 18 yrs) based on cycle 1 DLTs in up to 6 evaluable patients <18 yrs of age. Part B will estimate the antitumor activity of tiragolumab in combination with atezolizumab (15 mg/kg [max 1200 mg]) if < 18 yrs or 1200 mg if ≥ 18 yrs) in 6 histology-specific cohorts (renal medullary carcinoma, malignant rhabdoid tumor, atypical teratoid rhabdoid tumor, poorly differentiated carcinoma, epithelioid sarcoma, and other) Each cohort will be conducted using a 6+4 Simon’s two stage design. Up to 13 patients may enroll in each cohort allowing for inevaluable patients (maximum n=78). Enrollment of patients ≥ 18 yrs on Part B may occur concurrently with enrollment of patients < 18 yrs on Part A. If the pediatric dose of tiragolumab is deemed safe, patients <18 yrs old may be enrolled on Part B. Cycle 1 toxicities of the combination therapy will be monitored in Part B using a Bayesian Optimal Interval Design in patients < 12 yrs of age. The secondary objectives are to characterize pharmacokinetics/anti-drug antibody and estimating progression free survival, overall survival, and duration of response. Enrollment is open for all Pediatric Early Phase Clinical Trial Network sites. Clinical trial information: NCT05286801 .

A phase 2 study of sirolimus in combination with metronomic chemotherapy (CHOAnome) in children with recurrent and/or refractory solid and CNS tumors.

10024 Background: Multiple low-dose, anti-angiogenic (metronomic) chemotherapy regimens have demonstrated activity in pediatric solid and central nervous system (CNS) tumors. The mTOR pathway is activated in many human cancers and provides an attractive therapeutic target. We previously conducted a phase 1 trial establishing the dose (2 mg/m2), safety and tolerability of sirolimus in combination with metronomic chemotherapy. In the current study, we conducted a prospective, multi-institutional phase 2 trial to determine the objective response rate (ORR) in pediatric patients with recurrent and/or refractory (R/R) solid and CNS tumors treated with this regimen (NCT02574728); herein we report the results of the CNS tumor stratum. Methods: Patients aged 12 months to 30 years with R/R CNS tumors of all world health organization (WHO) grades were eligible. After completion of the trial’s first stage, patients with diffuse intrinsic pontine glioma (DIPG) were excluded due to lack of efficacy. Patients were required to have measurable disease and no known curative therapeutic options. Treatment consisted of continuous sirolimus (2 mg/m2/dose PO daily), celecoxib (100 mg PO BID), and oral etoposide (50 mg/m2/day; max dose: 100 mg) alternating every 21 days with oral cyclophosphamide (2.5 mg/kg/day; max dose: 100 mg) in 42-day cycles. Sirolimus was dose-adjusted to maintain a serum trough concentration of 10-15 ng/ml. Response was determined using a modified Response Assessment in Neuro-Oncology (RANO) criteria. Enrollment proceeded using a Fleming’s two-stage design based on best overall response (BOR), which required two objective disease status determinations. Results: Twenty-two CNS tumor patients were enrolled; 20/22 were evaluable for response. Median age was 11.2 years (range: 5.9 – 18.1); 6 (30%) were female. Diagnoses included DIPG (N = 5), medulloblastoma (N = 3), high-grade (HG) glioma (N = 5), HG/malignant neuroepithelial tumor (N = 3) and one each of diffuse midline glioma, atypical teratoid/rhabdoid tumor (ATRT), choroid plexus carcinoma, and pineoblastoma. Median number of cycles was 2 (range: 1-6). Best response after any cycle was partial response (PR) in 4 [medulloblastoma (N = 3); pineoblastoma (N = 1)], stable disease (SD) in 4, and progressive disease (PD) in 12 for an ORR of 20%; all patients with DIPG had PD at or before their first disease evaluation. BOR was PR in 3 (15%), SD in 2 (10%), PD in 14 (70%), and unknown in 1 (5%). Four patients had SD or response for ≥ 6 months [medulloblastoma (n = 1), pineoblastoma (N = 1), and HG glioma (N = 2)]. Conclusions: The combination of sirolimus with metronomic chemotherapy showed activity in pediatric patients with some R/R CNS tumors, producing objective responses in medulloblastoma and pineoblastoma. Patients with DIPG did not benefit from this regimen and should be offered alternative treatments. Clinical trial information: NCT02574728 .

Tazemetostat for tumors harboring SMARCB1/SMARCA4 or EZH2 alterations: results from NCI-COG pediatric MATCH APEC1621C.

National Cancer Institute-Children's Oncology Group Pediatric Molecular Analysis for Therapy Choice assigns patients aged 1-21 years with refractory solid tumors, brain tumors, lymphomas, and histiocytic disorders to phase II trials of molecularly targeted therapies based on detection of predefined genetic alterations. Patients whose tumors harbored EZH2 mutations or loss of SMARCB1 or SMARCA4 by immunohistochemistry were treated with EZH2 inhibitor tazemetostat. Patients received tazemetostat for 28-day cycles until disease progression or intolerable toxicity (max 26 cycles). The primary endpoint was objective response rate; secondary endpoints included progression-free survival and tolerability of tazemetostat. Twenty patients (median age = 5 years) enrolled, all evaluable for response and toxicities. The most frequent diagnoses were atypical teratoid rhabdoid tumor (n = 8) and malignant rhabdoid tumor (n = 4). Actionable alterations consisted of SMARCB1 loss (n = 16), EZH2 mutation (n = 3), and SMARCA4 loss (n = 1). One objective response was observed in a patient with non-Langerhans cell histiocytosis with SMARCA4 loss (26 cycles, 1200 mg/m2/dose twice daily). Four patients with SMARCB1 loss had a best response of stable disease: epithelioid sarcoma (n = 2), atypical teratoid rhabdoid tumor (n = 1), and renal medullary carcinoma (n = 1). Six-month progression-free survival was 35% (95% confidence interval [CI] = 15.7% to 55.2%) and 6-month overall survival was 45% (95% CI = 23.1% to 64.7%). Treatment-related adverse events were consistent with prior tazemetostat reports. Although tazemetostat did not meet its primary efficacy endpoint in this population of refractory pediatric tumors (objective response rate = 5%, 90% CI = 1% to 20%), 25% of patients with multiple histologic diagnoses experienced prolonged stable disease of 6 months and over (range = 9-26 cycles), suggesting a potential effect of tazemetostat on disease stabilization.

Survival benefit of postoperative radiotherapy for pediatric patients with primary intracranial atypical teratoid/rhabdoid tumors: Propensity score analysis and prediction model construction in a multi-registry based cohort

BackgroundThe role of postoperative radiotherapy (PORT) in children with primary intracranial atypical teratoid/rhabdoid tumor (AT/RT) remains controversial, and real-world data with large sample size are still lacking. This study aims to estimate the survival benefit of PORT in pediatric patients with resected AT/RT. MethodsUsing Seer database, we collected 246 eligible intracranial AT/RT patients diagnosed between 2000 and 2016 for our analysis. Propensity score matching (PSM) analysis was employed to minimize selection bias for evaluation of the PORT efficacy. Multivariate Cox regression was conducted to determine the factors related to the outcome. Interaction tests were further performed between PORT and the prognostic variables. After identifying the significant prognostic factors, we further developed a novel prediction model to predict the life expectancy of these patients, as well as the potential benefit from PORT. ResultsWe found that PORT was significantly related to the improved survival after adjusting for other prognosticators in both the entire and PSM-matched cohort. Significant interactions of PORT with age at diagnosis and tumor extension were also observed. On basis of the prognostic indictors identified by L1-penalized lasso Cox regression analysis, a novel nomogram model was successfully established and externally validated. ConclusionOur study indicated that PORT was significantly associated with the improved survival in pediatric AT/RT patients, and the greater survival benefit from PORT could be achieved in patients <3 years old or with locoregional tumors. The novel prediction model was developed to provide help in clinical practice and in the design of related trials.

Prognostic factors of pediatric pineal region tumors at a single institution.

This study aimed to identify factors of a worse prognosis among different histological types of pineal region tumors in pediatric patients treat at a single institution in a 30-year period. Pediatric patients (151; < 18years of age) treated between 1991 and 2020 were analyzed. Kaplan-Meyer survival curves were created, and the log-rank test was used to compare the main prognostic factors in the different histological types. Germinoma was found in 33.1%, with an overall 60-month survival rate of 88%; the female sex was the only factor of a worse prognosis. Non-germinomatous germ cell tumors were found in 27.1%, with an overall 60-month survival rate of 67.2%; metastasis upon diagnosis, residual tumor, and the absence of radiotherapy were associated with a worse diagnosis. Pineoblastoma was found in 22.5%, with an overall 60-month survival rate of 40.7%; the male sex was the only factor of a worse prognosis; a tendency toward a worse outcome was found in patients < 3years of age and those with metastasis upon diagnosis. Glioma was identified in 12.5%, with an overall 60-month survival rate of 72.6%; high-grade gliomas were associated with a worse prognosis. Atypical teratoid rhabdoid tumors was found in 3.3%, and all patients died within a 19-month period. Pineal region tumors are characterized by the heterogeneity of histological types, which exert an influence on the outcome. Knowledge of the prognostic factors for each histological types is of extreme importance to the determination of guided multidisciplinary treatment.

Outcomes and surgical approaches for pineal region tumors in children: 30 years' experience.

Pineal region tumors account for 2.7%-11% of all CNS tumors in children. In this series, the authors present their surgical results and long-term outcomes from a pediatric pineal region tumor cohort. A total of 151 children aged 0-18 years were treated from 1991 to 2020. Tumor markers were collected in all patients; if positive, chemotherapy was performed, and if negative, biopsy was performed, preferably endoscopically. Resection was performed when there was a residual germ cell tumor (GCT) lesion after chemotherapy. The distribution based on histological type, as verified by markers, biopsy, or surgery, was germinoma (33.1%), nongerminomatous GCT (NGGCT) (27.2%), pineoblastoma (22.5%), glioma (12.6%), and embryonal tumor (atypical teratoid rhabdoid tumor) (3.3%). A total of 97 patients underwent resection, and gross-total resection (GTR) was achieved in 64%; the highest GTR rate (76.6%) was found in patients with GCTs, and the lowest (30.8%) was found in those with gliomas. The supracerebellar infratentorial approach (SCITA) was the most common, performed in 53.6% of patients, followed by the occipital transtentorial approach (OTA), performed in 24.7% of patients. Lesions were biopsied in 70 patients, and the diagnostic accuracy was 91.4. The overall survival (OS) rates at 12, 24, and 60 months as stratified by histological type were 93.7%, 93.7%, and 88% for patients with germinomas; 84.5%, 63.5%, and 40.7% for patients with pineoblastomas; 89.4%, 80.8%, and 67.2% for patients with NGGCTs; 89.4%, 78.2%, and 72.6% for patients with gliomas; and 40%, 20%, and 0% for patients with embryonal tumors, respectively (p < 0001). The OS at 60 months was significantly higher in the group with GTR (69.7%) than in the group with subtotal resection (40.8%) (p = 0.04). The 5-year progression-free survival was 77% for patients with germinomas, 72.6% for patients with gliomas, 50.8% for patients with NGGCTs, and 38.9% for patients with pineoblastomas. The efficacy of resection varies by histological type, and complete resection is associated with higher OS rates. Endoscopic biopsy is the method of choice for patients presenting with negative tumor markers and hydrocephalus. For tumors restricted to the midline and with extension to the third ventricle, a SCITA is preferred, whereas for lesions with extension toward the fourth ventricle, an OTA is preferred.

Consensus recommendations on counselling in Phelan-McDermid syndrome, with special attention to recurrence risk and to ring chromosome 22

This paper focuses on genetic counselling in Phelan-McDermid syndrome (PMS), a rare neurodevelopmental disorder caused by a deletion 22q13.3 or a pathogenic variant in SHANK3. It is one of a series of papers written by the European PMS consortium as a consensus guideline. We reviewed the available literature based on pre-set questions to formulate recommendations on counselling, diagnostic work-up and surveillance for tumours related to ring chromosome 22. All recommendations were approved by the consortium, which consists of professionals and patient representatives, using a voting procedure. PMS can only rarely be diagnosed based solely on clinical features and requires confirmation via genetic testing. In most cases, the family will be referred to a clinical geneticist for counselling after the genetic diagnosis has been made. Family members will be investigated and, if indicated, the chance of recurrence discussed with them. Most individuals with PMS have a de novo deletion or a pathogenic variant of SHANK3. The 22q13.3 deletion can be a simple deletion, a ring chromosome 22, or the result of a parental balanced chromosomal anomaly, influencing the risk of recurrence. Individuals with a ring chromosome 22 have an increased risk of NF2-related schwannomatosis (formerly neurofibromatosis type 2) and atypical teratoid rhabdoid tumours, which are associated with the tumour-suppressor genes NF2 and SMARCB1, respectively, and both genes are located on chromosome 22. The prevalence of PMS due to a ring chromosome 22 is estimated to be 10–20%. The risk of developing a tumour in an individual with a ring chromosome 22 can be calculated as 2–4%. However, those individuals who do develop tumours often have multiple. We recommend referring all individuals with PMS and their parents to a clinical geneticist or a comparably experienced medical specialist for genetic counselling, further genetic testing, follow-up and discussion of prenatal diagnostic testing in subsequent pregnancies. We also recommend karyotyping to diagnose or exclude a ring chromosome 22 in individuals with a deletion 22q13.3 detected by molecular tests. If a ring chromosome 22 is found, we recommend discussing personalised follow-up for NF2-related tumours and specifically cerebral imaging between the age of 14 and 16 years.

Focal versus craniospinal radiation for disseminated atypical teratoid/rhabdoid tumor following favorable response to systemic therapy.

Radiotherapy (RT) is associated with improved survival in atypical teratoid/rhabdoid tumor (ATRT); however, optimal RT delivery is unknown. A meta-analysis was conducted for disseminated (M+) ATRT receiving focal or craniospinal radiation (CSI). After abstract screening, 25 studies (1995-2020) contained necessary patient, disease, and radiation treatment information (N=96). All abstract, full text, and data capture were independently double-reviewed. The corresponding author was contacted for cases of insufficient information. Response to pre-radiation chemotherapy (N=57) was categorized as complete response (CR), partial response (PR), stable disease (SD), and progressive disease (PD). Univariate and multivariate statistics were performed to investigate survival correlation. Patients with M4 disease were excluded. The 2- and 4-year overall survival (OS) was 63.8% and 45.7%, respectively, with a median follow-up of 2years (range 0.3-13.5). The median age was 2years (range 0.2-19.5), and 96% received chemotherapy. On univariate analysis, gross total resection (GTR, p=.0007), pre-radiation chemotherapy response (p<.001), and high-dose chemotherapy with stem cell recuse (HDSCT, p=.002) correlated with survival. On multivariate analysis, pre-radiation chemotherapy response (p=.02) and GTR (p=.012) retained survival significance as compared to a trend for HDSCT (p=.072). Comparisons of focal RT (vs. CSI) and greater than or equal to 5400cGy primary dose were nonsignificant. Following CR or PR, a statistical trend favored focal radiation (p=.089) over CSI. Chemotherapy response prior to RT and GTR correlated with improved survival on multivariate analysis for ATRT M+ receiving RT. No benefit was observed for CSI compared to focal RT among all patients and following favorable chemotherapy response, inviting further study of focal RT for ATRT M+.

Clinical and histopathological spectrum of cranial small round cell tumors: An experience from a tertiary care center.

Small round cell tumors (SRCTs) are a group of malignant neoplasms with minimal or no differentiation, characterized by the presence of round cells with high nuclear-cytoplasmic ratio. Although SRCTs can occur in any part of the body, involvement of central nervous system (CNS) is uncommon. We aimed to study the clinicopathological spectrum of cranial SRCT diagnosed in our institute over a period of four years (2016-2019). A retrospective review of medical records (2016-2019) with a morphological diagnosis of cranial SRCT was made. Both intra-axial and extra-axial tumors were included. A total of 60 cases were retrieved, and the clinical and histopathological features were studied. Special cytochemical staining and immunohistochemistry were performed, where needed. The mean age at presentation was 18.4 years (range, 1-60 years), with a male-to-female ratio of 2.5:1. The most common site was posterior fossa of brain (n = 28, 47%), followed by dorso-lumbar spine (n = 9, 15%). The most common type of tumor was medulloblastoma (n = 29, 48.3%), followed by Ewing sarcoma (ES)/peripheral primitive neuroectodermal tumor (pPNET) (n = 11, 18.3%), non-Hodgkin lymphoma (NHL) (n = 9, 15%), neuroblastoma (n = 3, 5%), and CNS embryonal tumor, NOS (n = 2, 3.3%). One case each of atypical teratoid rhabdoid tumor (ATRT), rhabdomyosarcoma, pineoblastoma, melanoma, rhabdomyosarcoma, and undifferentiated pleomorphic sarcoma was also documented. SRCTs have a variable age of presentation. Their incidence in CNS is low as compared to other organ systems. On light microscopy, the histopathology of these lesions is overlapping, posing a great diagnostic dilemma for the pathologist. The use of ancillary techniques like immunohistochemistry helps in arriving at the correct diagnosis. Treatment strategy and tumor prognosis also vary along the entire spectrum of SRCT, thus making exact characterization essential for proper management.

Atypical teratoid/rhabdoid tumoroids reveal subgroup-specific drug vulnerabilities

Atypical teratoid/rhabdoid tumors (ATRTs) represent a rare, but aggressive pediatric brain tumor entity. They are genetically defined by alterations in the SWI/SNF chromatin remodeling complex members SMARCB1 or SMARCA4. ATRTs can be further classified in different molecular subgroups based on their epigenetic profiles. Although recent studies suggest that the different subgroups have distinct clinical features, subgroup-specific treatment regimens have not been developed thus far. This is hampered by the lack of pre-clinical in vitro models representative of the different molecular subgroups. Here, we describe the establishment of ATRT tumoroid models from the ATRT-MYC and ATRT-SHH subgroups. We demonstrate that ATRT tumoroids retain subgroup-specific epigenetic and gene expression profiles. High throughput drug screens on our ATRT tumoroids revealed distinct drug sensitivities between and within ATRT-MYC and ATRT-SHH subgroups. Whereas ATRT-MYC universally displayed high sensitivity to multi-targeted tyrosine kinase inhibitors, ATRT-SHH showed a more heterogeneous response with a subset showing high sensitivity to NOTCH inhibitors, which corresponded to high expression of NOTCH receptors. Our ATRT tumoroids represent the first pediatric brain tumor organoid model, providing a representative pre-clinical model which enables the development of subgroup-specific therapies.

Abstract 3933: RRM2 inhibition by COH29 is a potential therapeutic strategy for atypical teratoid rhabdoid tumors

Abstract Introduction: Atypical teratoid rhabdoid tumors (ATRT) are a rare but aggressive malignancy in central nervous system, commonly occurring in early childhood. ATRT patients face a dismal prognosis despite aggressive therapy. Development of both effective and protective targeted therapy is an emerging necessity. It has been reported that RRM2 is a master driver of aggressiveness and a poor prognosis biomarker in several cancers. However, little is known about RRM2 function in ATRT. The aim of this study is to assess the roles of RRM2 in ATRT and elucidate the therapeutic potential of RRM2 to cure the 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 3 different cell lines to elucidate the oncogenic role of RRM2 in ATRT cells. The efficacy of COH29, an RRM2 inhibitor, was assessed in vitro. ATRT model of SCID mice orthotopically injected with ATRT cells were used to test the efficiency of COH29 for in vivo. Western blot and RNA-sequencing were used to determine the mechanisms of RRM2 transcriptional activation in ATRT. Results: Molecular profiling results revealed that RRM2 was relatively highly expressed in ATRT tissues and cell lines. Clinical relevance analysis results showed that the RRM2 expression level was associated with poor prognosis among ATRT patients. Knockdown of RRM2 by shRNAs significantly reduced ATRT cells colonies formation, proliferation and migration. A similar but more pronounced inhibitory effect was observed when COH29 was used to target RMM2. Inhibition of RRM2 by shRNAs or COH29 significantly induced cell death via DNA damage and/or apoptosis pathways. In vivo results demonstrated that COH29 could suppressed ATRT tumor growth and extend mice overall survival. Conclusion: Our study identified RRM2 as a potential mediator of oncogenic cellular functions in ATRT cell lines. We propose that highly expressed RRM2 is associated with poor patient outcomes, and inhibition of RRM2 by COH29 may present a significant therapeutic value in ATRT. Citation Format: Le Hien Giang, Tai-Tong Wong, Che- Chang. RRM2 inhibition by COH29 is a potential therapeutic strategy for atypical teratoid rhabdoid tumors. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3933.

Abstract 4875: The anti-tumor effects of GSK-3β inhibitor (9-1NG-41) in ETMR and ATRT pediatric brain tumors

Abstract Purpose Embryonal brain tumors (EBTs): ETMR (embryonal tumor with multilayered rosettes) and ATRT (atypical teratoid rhabdoid tumor) are aggressive malignancies with poor prognosis necessitating alternative strategies. GSK-3β is a serine threonine kinase often overexpressed in solid tumors and a positive regulator of NF-κB which promotes tumor growth and chemotherapy resistance. 9-ING-41 is a maleimide-based small molecule that crosses the blood brain barrier and selectively inhibits GSK-3β. Previously we demonstrated that 9-ING-41 decreases ETMR and ATRT cell viability through apoptosis and increases p53 signaling, however the exact mechanism leading to its activation is unknown. This study aims to determine the optimal dosing for 9-ING-41 and describe the phenotypic response of these cell lines to 9-ING-41 using cell viability assay, western blotting and neurosphere assay. This information will help further elucidate the mechanism of action for this drug. Methods ATRT cell lines ATRT 2141, ATRT-787199, ATRT 803499, LCH-091-07 and the ETMR cell line BT-183 were grown for 24hrs prior to 9-ING-41 treatment in DMEM and Neurocult medium, respectively. Cell viability was assessed after 72hrs of treatment using Cell Titer Glo 2.0. Western blots were analyzed for XIAP, cleaved caspase-3, p53, MDM2 after 24 and 48 hours at 200nM, 400nM and 600nM. Neurosphere assays were done by seeding two cells per well in a 96-well plate followed by treatment with 9-ING-41. Neurosphere frequency and size was monitored weekly for up to 4 weeks using Incucyte® S3 software. Pearson’s correlation graph was generated to determine the relationship between GSK-3β expression and sensitivity to 9-ING-41. Graph Pad Prism was used for statistical analysis and level of significance set to p=0.05. Results The IC50s of 9-ING-41 in cell lines ATRT 2141, ATRT-787199, ATRT 803499 and LCH-091-07 were 194nM, 558nM, 730nM &amp; 5353nM, respectively. We observed decreased expression of NF-κB mediated anti-apoptotic marker XIAP and an increase in expression of apoptotic marker cleaved caspase-3 and tumor suppressor p53 in response to 9-ING-41. MDM2, a negative regulator of p53 had a significant increase in expression indicating it is not responsible for p53 increase which may suggest ATM pathway could be responsible for regulating p53 increase. GSK-3β expression in vitro, correlated with sensitivity to 9-ING-41. There was a dose dependent decrease in frequency and size of neurospheres in response to 9-ING-41. Conclusion 9-ING-41 decreases cell viability and neurosphere formation in ETMR and ATRT cell lines within clinically relevant doses. p53 stabilization is not mediated by MDM2 and may be downstream of the ATM pathway. Further studies are underway to demonstrate its efficacy in mouse models. Citation Format: Divya Gandra, Lauren Difabio, Kaitlyn H. Smith, Kimberly Q. McKinney, Giselle S. Sholler. The anti-tumor effects of GSK-3β inhibitor (9-1NG-41) in ETMR and ATRT pediatric brain tumors. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4875.