Neurofibromatosis Research Articles

Gene Mutations in Gastrointestinal Stromal Tumors: Advances in Treatment and Mechanism Research.

Although gastrointestinal stromal tumors (GISTs) has been reported in patients of all ages, its diagnosis is more common in elders. The two most common types of mutation, receptor tyrosine kinase (KIT) and platelet-derived growth factor receptor a (PDGFRA) mutations, hold about 75 and 15% of GISTs cases, respectively. Tumors without KIT or PDGFRA mutations are known as wild type (WT)-GISTs, which takes up for 15% of all cases. WT-GISTs have other genetic alterations, including mutations of the succinate dehydrogenase and serine-threonine protein kinase BRAF and neurofibromatosis type 1. Other GISTs without any of the above genetic mutations are named "quadruple WT" GISTs. More types of rare mutations are being reported. These mutations or gene fusions were initially thought to be mutually exclusive in primary GISTs, but recently it has been reported that some of these rare mutations coexist with KIT or PDGFRA mutations. The treatment and management differ according to molecular subtypes of GISTs. Especially for patients with late-stage tumors, developing a personalized chemotherapy regimen based on mutation status is of great help to improve patient survival and quality of life. At present, imatinib mesylate is an effective first-line drug for the treatment of unresectable or metastatic recurrent GISTs, but how to overcome drug resistance is still an important clinical problem. The effectiveness of other drugs is being further evaluated. The progress in the study of relevant mechanisms also provides the possibility to develop new targets or new drugs.

Appendiceal neurofibroma after resection of multiple gastrointestinal stromal tumors of the small intestine in a patient with neurofibromatosis type 1: a case report.

Neurofibromatosis type 1 (NF1), also known as von Recklinghausen disease, is an autosomal dominant disorder that can affect multiple organs. Although gastrointestinal manifestations, such as neurofibromas and gastrointestinal stromal tumors (GISTs), can occur, appendiceal neurofibromas are extremely rare, with no documented cases of their occurrence following other gastrointestinal lesions. Herein, we report a case of an appendiceal neurofibroma following the resection of multiple small intestinal GISTs. A 68-year-old man with NF1 presented with melena and was diagnosed with anemia due to bleeding from multiple small intestinal GISTs. Laparoscopic three partial resection of the small intestine was performed to control the bleeding. Histopathologic examination revealed the proliferation of spindle cells that are positive for c-kit and Discovered on GIST-1, confirming the diagnosis of GIST. Two years later, a follow-up computed tomography (CT) scan revealed a progressively enlarging mass in the appendix with suspected invasion into the small intestine. Positron emission tomography/CT showed fludeoxyglucose accumulation in the tumor. Therefore, considering the possibility of malignancy, laparoscopic ileocecal resection with lymph node dissection was performed. Postoperatively, melena was observed, but the anemia did not progress and improved with fasting and hemostatic therapy. The patient was eventually discharged on postoperative day 8. Histopathologic examination revealed spindle cell proliferation with positivity for S-100, confirming the diagnosis of neurofibroma. Patients with NF1 can develop a variety of gastrointestinal lesions. Appendiceal neurofibroma can be difficult to diagnose preoperatively and differentiate from malignancy. Hence, surgical resection should be considered.

Phaeochromocytoma associated with neurofibromatosis type 1: a single tertiary care centre experience

Phaeochromocytoma associated with neurofibromatosis type 1: a single tertiary care centre experience

Altered body as a source of interactional problems in the family of individuals with neurofibromatosis type 1 - A polish study.

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic disorder, whose clinical picture is dominated by visible body changes as well as numerous somatic and behavioural abnormalities. The aim of the study was to explore the ways in which the individual experiences NF1 in everyday life, with particular emphasis on the impact of the altered body on family interactions, in addition to the personal and social identity of individuals with NF1. A qualitative study was performed using individual in-depth interviews with 93 individuals with NF1 (median age: 36.69; range: 18 to 64; 26% males). Body changes caused by NF1 determine the specificity of social interactions in the families of the sick. The strength and direction of the impact of body changes on social interactions depends on their type (visibility, invisibility), as well as the meanings given to them. The visibility of disease lesions triggers an attitude of excessive control and stigmatization in the family, especially on the part of the mothers of individuals with NF1, and prompts a tendency to define the individual through the prism of the disease and its bodily manifestations. In turn, the lack of visibility of disease symptoms gives rise to, especially on the part of the fathers of the sick, opposing attitudes of disease denial, normalization of its symptoms and a tendency to question the disease identity of individuals with NF1. The great intensity of interactional problems concerns especially those families in which NF1 was transmitted through inheritance, and family members blame each other for the disease. This leads to repression and denial of the disease, excluding it from the scope of issues discussed in the family, which is an attempt to avoid the attribution of blame for the disease. The body changes resulting from NF1 have social consequences that are of critical importance in the lives of the sick. The impact of NF1 on family interactions depends on the ways in which the disease is understood by the sick individual and his or her family members. The obtained patient-driven data constitute a convenient starting point for designing personalized interventions supporting individuals with NF1 and their families.

TMOD-26. GENERATION OF A CHROMOSOME 8 GAIN;NF1-/- HIPSC-DERIVED SCHWANN CELL PRECURSOR MODEL

Abstract Neurofibromatosis type 1 (NF1) is an autosomal dominant cancer predisposition syndrome caused by a germline mutation in the NF1 gene. The loss of the second copy of NF1 within Schwann cell precursors (SCPs) contributes to the formation of plexiform neurofibromas (PNs) found in 30-50% of NF1 patients. PNs can progress into malignant peripheral sheath tumors (MPNSTs), an aggressive form of cancer and a leading cause of mortality in NF1 patients. Our lab previously demonstrated frequent chromosome 8 (Chr8) gain in NF1-MPNST patient-derived xenografts (PDX) and patient tumors. To investigate Chr8 gain’s role, we created isogenic NF1-/- iPSC cell lines with and without Chr8 gain. Trisomy 8 fibroblasts were obtained and single-cell cloned to establish wildtype (WT) and Chr8 gain populations. Washington University’s Genome Engineering & Stem Cell Center (GESC@MGI) reprogrammed these cells into human induced pluripotent stem cells (hiPSCs). Using synthetic gRNA and CRISPR/Cas9, NF1 knockout lines were generated. Four iPSC cell lines were differentiated into SCPs, and cell survival and proliferation were assessed using Incucyte cell survival and CellTiter-Glo® Assay. Fluorescence in situ hybridization (FISH) and karyotyping validated the human iPSCs. qPCR revealed high expression of iPSC markers OCT3/4 and SOX2 in all iPSC lines. After differentiation, SCP markers (GAP43 and ITGA4) were upregulated in WT, NF1-/-, and Chr8 gain;NF1-/- SCP lines, demonstrating successful differentiation. Furthermore, Chr8 gain; NF1-/- SCPs displayed enhanced proliferation and increased cell survival compared to WT and NF1-/- SCPs, suggesting improved characteristics in the presence of Chr8 gain. In summary, our research provides insights into Chr8 gain and NF1 loss effects on SCP differentiation, proliferation, and survival. Understanding these molecular mechanisms may contribute to developing targeted therapies for NF1.

QOL-30. DIETARY CONSIDERATIONS FOR PEOPLE WITH NF1: A SYSTEMATIC REVIEW OF THE LITERATURE

Abstract BACKGROUND Neurofibromatosis type 1 (NF1) is a neurocutaneous genetic condition. Limited pre-clinical and clinical data suggests that certain metabolic disturbances, body composition differences and nutritional deficiencies may be more prevalent in people with NF1. Data on the role of dietary patterns in people with NF1 and their effects in NF1-related manifestations is scarce. METHODS A systematic literature review was conducted; the MeSH database of PubMed was utilized to identify controlled vocabulary and key words associated with NF1, diet, and nutrition. These terms were combined using boolean operators to query PubMed, Embase, PLOS One, and Cochrane. The inclusion criteria consisted of articles in English, full text available, human studies, published between 2000-2024. The results were screened and key details were extracted. RESULTS 394 published articles were identified, out of which 15 met the inclusion criteria. 379 papers were excluded due to duplication or not meeting all inclusion criteria. Manuscripts included case reports, case series, retrospective and prospective studies, including a phase 2a clinical trial that only included six participants. Topics included vitamin D and bone metabolism, nutritional supplements, glucose metabolism, and nutritional intake. CONCLUSIONS Data regarding the effects of diet or nutritional supplements in people with NF1 is limited. Available studies suggest that a diet composed of therapeutic elements, including but not limited to, medium-chain fatty acids, calcium, and vitamin D, aids in bone growth and density, and muscle lipolysis. A single clinical trial suggests that L-carnitine supplementation is safe and feasible and might result in improved functional muscle performance in children with NF1. These conclusions might only be applicable to a small population of people with NF1 and did not result in conclusive significant clinical benefit. Further research is needed to better comprehend the role that nutrition plays in patients’ quality of life.

CNSC-07. OLIGODENDROGLIAL IMPAIRMENT IN WHITE MATTER TRACTS FOLLOWING NEUROFIBROMATOSIS TYPE 1 (NF1) GERMLINE MUTATION OR CARBOPLATIN TREATMENT

Abstract Neurofibromatosis type 1 (NF1) is a cancer predisposition syndrome due to mutations in the NF1 gene. The disease affects 1 in 2500-3000 people worldwide and patients are predisposed to neoplasms such as optic pathway glioma, plexiform neurofibroma. In addition, NF1 patients often experience neurological issues such as learning difficulties. Unfortunately, there is no cure for NF1 yet. Chemotherapy (e.g., carboplatin) remains the first-line treatment for NF1-associated low-grade glioma; while effective in reducing tumor burden, it does not reliably restore neuronal function. In this study, we sought to determine how chemotherapy and Nf1 germline mutations influence neurological function, using genetically engineered mice of NF1. Nf1-heterozygous mice received carboplatin (60 mg/kg/day) or vehicle every other day for one week. Their optic nerves were collected and processed for immunofluorescence and transmission electron microscopy (EM). We found that carboplatin treatment reduces the density of oligodendrocytes in Nf1-heterozygous mice and impairs myelination. Moreover, a similar effect of carboplatin was observed in wild-type mice, suggesting that carboplatin impairs oligodendroglia independent of the NF1 status and the effect of carboplatin should also be evaluated in the non-NF1 context. In another set of experiments, we sought to understand how germline Nf1 mutations influences oligodendroglia. Whereas we did not observe a difference in optic nerve oligodendrocyte density in mice with an engineered mutation targeting the GTPase-activating protein-related domain (GRD) domain of the Nf1 gene, a reduction of oligodendrocyte density was observed in mice harboring a patient-derived mutation (R1809C), which localizes outside of the GRD. A similar effect was observed in the corpus callosum of Nf1+/R1809C mice together with myelin impairment, suggesting a RAS-independent mechanism of Nf1 regulation of oligodendrocytes. Together, these findings indicate that both Nf1 germline mutations and chemotherapy could contribute to oligodendrocyte and myelin deficits in white matter tracts.

EPCO-59. FIRST CASE REPORT OF COMBINED GERMLINE NF1 AND BRCA2 MUTATIONS PRESENTED WITH NEUROFIBROMAS AND LIPOMATOSIS

Abstract Both Neurofibromatosis type 1(NF1) and BRCA2 are common tumor suppressor genes, with mutations in each associated with genetic tumor syndromes. However, it is extremely rare to observe two different germline mutations in one patient. To the author’s knowledge, this is the first case report of a patient with germline mutations in both pathological NF1 and BRCA2 genes. We report a 41-year-old male patient with neurofibromas and lipomatosis. The patient with known family history of NF1, was diagnosed with NF1 after skin biopsy at 28 years old. At 40 years old, he underwent resection of a large intrathoracic neurofibroma. For genetic confirmation, next generation sequencing test was performed on both the intrathoracic neurofibroma tumor sample and saliva sample, revealing unexpected pathological germline mutation in both NF1 and BRCA2 genes. Consequently, the patient underwent resection of multiple lesions in the chest, abdomen, and upper extremities due to concern for potential breast cancers, and pathology of these lesions predominantly showed lipomas and one angiolipoma. Patient has family members with NF1 including a maternal aunt, a maternal cousin, and one son. However, there is no family history of lipomatosis or cancers commonly associated with BRCA2 mutation such as breast, ovarian, pancreatic, or prostate cancer. While lipomas are reported in patients with NF1, it is unusual that patient does not have typical café-au-lait spots or multiple neurofibromas but instead has multiple lipomas. This unusual presentation may be related to his unique genetic condition involving germline mutations in two tumor suppressor genes. Long term follow-up with screening tests for known tumors associated with each genetic mutation will be essential.

INNV-12. CUTANEOUS TOXICITIES OF MITOGEN-ACTIVATED PROTEIN KINASE INHIBITORS IN CHILDREN AND YOUNG ADULTS WITH NEUROFIBROMATOSIS-1

Abstract BACKGROUND Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder which commonly causes neoplasms leading to disfigurement or dysfunction. Mitogen-activated protein kinase inhibitors (MEKi) are generally well-tolerated treatments which target neural tumor progression in patients with NF1. Cutaneous adverse events (CAEs) are common and may hinder patients’ abilities to remain on treatment, particularly in children. We aim to characterize CAEs secondary to MEKi treatment in pediatric and young adult patients with NF1. METHODS We reviewed institutional medical records of patients under 30 years with a diagnosis of “NF1,” “NF2,” or “other neurofibromatoses” on MEKi therapy between January 1, 2019 and June 1, 2022. We recorded the time-to-onset, type, and distribution of CAEs, non-cutaneous adverse events (AEs), AE management, and tumor response. RESULTS The median age of 40 patients with NF1 was 14 years old. Tumor types included low-grade gliomas (51%) and plexiform neurofibromas (38%). MEKi used included selumetinib (69%), trametinib (25%), and mirdametinib (6%) (Table 1). A total of 74 CAEs occurred, with 28 cases of acneiform rash (38%) (Figure 1). Twenty-three out of the 28 cases of acneiform eruption were in post-pubertal patients (82.1%). Other common CAEs were paronychia, seborrheic dermatitis, eczema, xerosis, and oral mucositis. The most common treatments included oral antibiotics and topical corticosteroids. Most patients had clinical (stable or improved) tumor response (71%) while 29% had tumor progression while on a MEKi (Table 2). There was no significant association between CAE presence and tumor response (p=0.39). CONCLUSIONS MEK inhibitors have been demonstrated as a valuable treatment, but CAEs complicate the ability to stay on the treatment. Most patients in our cohort developed a CAE, demonstrating its prevalence in this population. Improvement in characterization of MEKi toxicities and their management is important to develop treatment guidelines for pediatric and young adult patients with NF1 on MEKi therapy.

EPCO-22. DEEP PHENOTYPING IDENTIFIES TRUNCATING MUTATIONS IN THE NF2 LINKER DOMAIN ASSOCIATED WITH DISEASE SEVERITY IN NEUROFIBROMATOSIS TYPE II

Abstract INTRODUCTION Neurofibromatosis type 2 (NF2) is an autosomal dominant tumor syndrome with protean presentation and variable penetrance. Our objective was to perform deep phenotypic and genetic analysis of a diverse NF2 population to identify predictors of worse clinical outcome. METHODS We evaluated 167 patients with NF2 and followed them for a mean duration of 4.5 years. Detailed clinical and radiographic characteristics were collected on each patient, and Karnofsky performance scale (KPS) scores and within-study mortality were monitored. CLIA certified genotyping was supplemented with a custom sequencing panel targeting NF2 and other schwannomatosis-related genes. Outcome predictors were assessed using multivariable linear or logistic regression. RESULTS Germline mutations (nonsense 36%, splice-site 16%, and large deletions 16%) were grouped by predicted protein effect (truncating 41%, non-truncating 27%, and mosaic 33%) and mapped to the NF2chromosomal locus. Patients with truncating NF2 mutations had lower mean age of diagnosis (19.9 versus 25.7, P = 0.01) and faster tumor growth rates (2.4% versus 1.1% for all tumors, P = 0.01). Patients whose truncating mutations occurred within the NF2 linker domain (exons 8, 11 and 12) had more total tumors (adjusted coefficient 15.0, 95% CI 0.8 – 29.0, P = 0.04), and specifically more schwannomas (adjusted coefficient 7.0, 95% CI 0.2 – 13.9, P = 0.04). Presence of a-helical domain mutations predicted higher within-study mortality (adjusted OR 4.3, 95% CI 1.1 – 16.2, P = 0.03). CONCLUSIONS The NF2 linker domain functions a hinge, facilitating binding between the tail domain and the LATS binding site within the FERM domain. In our study, truncating mutations in the NF2 linker domain were associated with higher tumor burden and over four-fold within-study mortality. The linker domain may constitute a novel therapeutic target in patients with NF2.

QLTI-13. A REVIEW OF THE BEST TREATMENT STRATEGY FOR NEUROFIBROMATOSIS TYPE 2 PATIENTS THROUGH A SINGLE-CENTER RETROSPECTIVE STUDY: HOW TO ORCHESTRATE MULTIMODAL TREATMENT OPTIONS

Abstract PURPOSE Neurofibromatosis type 2(NF2) is an autosomal-dominant tumor predisposition syndrome that affects the whole neuro-axis and causes various neurological symptoms decreasing the quality of life throughout the patient’s lifespan. However, due to the diversity of related diseases and the complexity of treatment, there are many cases in which only partial treatments are performed, the timing of the treatment is missed, and inappropriate treatment modality selection is made despite the intervention of many clinicians. Therefore, to increase the overall understanding of the disease, the single-institution experience was analyzed. MATERIALS AND METHODS Between 1998 and 2022, a total of 80 patients who clinically suspected NF2 visited our Brain Tumor Center. After excluding the patients with follow-up loss, the remaining 48 patients were finally analyzed. The patient’s symptoms, diagnosis process, treatment process, and outcomes were analyzed. RESULTS The average age at the time of symptom onset was 31.0(2-63) year-old. Hearing impairment was the major primary symptom(46.8%) among the patients. Five patients(10.9%) had family history of NF2. Thirty-five patients(76.1%) was clinically diagnosed as a NF2 for the bilateral vestibular schwannomas, and 34 patients(73.9%) had intracranial meningiomas, and 37 patients(80.4%) had spinal lesions at the time of diagnosis. Eleven patients were genetically confirmed as NF2. For vestibular schwannomas, 16 patients had surgical resection and 20 patients took gamma-knife surgery as a primary or secondary treatment. For intracranial meningiomas, 16 patients had surgical resection, 13 patients took gamma-knife surgery, and 15 patients took conventional radiation therapy as a primary or secondary treatment. Ventriculo-peritoneal shunt due to increased intracranial pressure was performed in 4 patients(8.7%). For spinal lesions, 16 patients had surgical resection. CONCLUSION NF2 is a disease group requiring a multidisciplinary team approach. The key to treatment is to set and implement a treatment sequence and method tailored to each patient. For this, an overall understanding of the disease and the treatment options is essential.

BIOS-02. DIFFERENT GROWTH PATTERN OF VESTIBULAR SCHWANNOMAS IN NEUROFIBROMATOSIS TYPE 2 PATIENTS ACCORDING TO AGE

Abstract The natural growth pattern of vestibular schwannoma (VS) associated with the rare disease neurofibromatosis type 2 (NF2) has not been sufficiently elucidated, and the rationale for proactive treatment for VS in NF2 is not firmly established. This study aimed to uncover the growth pattern of VS associated with NF2 and identify risk factors for rapid growth. A total of 68 VSs from 41 NF2 patients who were diagnosed in Seoul National University Bundang Hospital from July 2006 to July 2023 were retrospectively reviewed. NF2 was clinically diagnosed according to the Manchester criteria. The mean age was 34±16 years (mean ± standard deviation) at diagnosis. The initial tumor volume was a median of 0.263 cm³ (interquartile range [IQR], 0.053-0.754 cm³), and 51 VSs exhibited serviceable hearing classified as Gardner-Robertson grade 1 or 2. Patients were followed for a median of 45 months (IQR, 30-80 months), during which the median volume increased by 0.145 cm³ (IQR, 0.020-0.783 cm³), representing an annual growth rate of 0.044 cm³/yr (IQR, 0.003-0.202 cm³) or 12.4%/yr (IQR, 2.2-27.5%). Patients younger than 25 years (15 patients with 28 VSs) had significantly smaller initial tumor sizes (0.170 cm³ [IQR, 0.031-0.339 cm³] vs. 0.510 cm³ [0.099-1.399 cm³]) but faster tumor growth rates (annual growth rate; 27.3%/yr [IQR, 11.3-81.4%/yr] vs. 4.7%/yr [IQR, 0.0-16.1%/yr]) compared to those 25 years or older (26 patients with 40 VSs). Among the 51 VSs with serviceable hearing at diagnosis, 40 VSs were followed up for more than 12 months. Among them, 13 (32.5%) experienced unserviceable hearing deterioration at a median of 58 months. The risk of hearing loss significantly increased with faster tumor growth rates. The growth rate of NF2-related VS was higher in patients under the age of 25, which may be helpful in determining indications for proactive treatments like radiosurgery for NF2-related VS.

CSIG-19. IDENTIFICATION AND TARGETING OF TUMOR DRIVER SCHWANN(NF2LOSS) CELLS IN SPORADIC AND NF2-RELATED VESTIBULAR SCHWANNOMAS

Abstract Vestibular schwannomas (VS) arise from myelinating Schwann cells of CN VIII and are associated with severe morbidity due to local tumor growth. Sporadic and neurofibromatosis type 2 (NF2) associated VS are both characterized by NF2 (merlin) loss but the mechanisms remain unexplored. Using a multiomic approach, we dissected the role of NF2 loss in VS tumor formation and proliferation. We obtained surgical samples from 15 patients undergoing surgery for VS (sporadic, n=4; NF2, n=9), and performed single-cell or single-nucleus RNA sequencing (scRNAseq, n=4; snRNAseq, n=15), transposase-accessible chromatin (snATAC-seq, n=9), whole exome (n=12), and bulk DNA methylation assays (n=15). Transcription factor binding was assayed with ChIPseq. We validated our key findings with immunoblot, ELISA, RNAscope (n=8), and multiplex immunocytochemistry (mIHC; n=8). NF2fl/fl;Periostin-Cre+mice versus their Cre- control littermates treated with novel inhibitors of TEAD auto-palmitoylation (VTs). We mapped the VS transciptome and identified canonical Schwann cells, macrophages, T-cells and endothelial cells. Using the cells that had Chr22 loss (second hit deletions at the NF2 locus), we generated a NF2loss gene signature. We then identified Schwann(NF2loss) cells in all tumors, and found these enriched for YAP1/TAZ-TEAD, NRG1, and HIF-1α signaling pathways. Schwann(NF2loss) cells showed increased TEAD1 expression and chromatin accessibility for TEAD family transcription factor motifs. TEAD1 binding was observed at promoters of genes including VEGFA, EGFR, with strong enrichment for mitogenic pathways. We also found that VEFGA expression was restricted to Schwann(NF2loss) cells, and confirmed this with RNAscope and mIHC. Schwann(NF2loss) cells were key regulators of macrophages (M2-subtype, tissue resident) through M-CSF/IL-34 signaling. NF2fl/fl;Periostin-Cre+ mice showed increased VEGFA expression, and that was reversible by TEAD inhibition in-vivo with VTs. We report that Schwann(NF2loss) cells are key tumor drivers in VS. These cells are highly proliferative (YAP/TAZ-TEAD axis), drive angiogenesis (VEGFA expression), and promote tumor mass accretion (macrophage influx via M-CSF/IL-34 pathway) that can all be targeted via TEAD inhibition.

PATH-38. INTRACRANIAL SARCOMA WITH DICER1 MUTATION IN A PATIENT WITH NEUROFIBROMATOSIS TYPE 1

Abstract A 16-year-old male with neurofibromatosis type 1 (NF1) and a history of low-grade gliomas presented for resection of a progressively enlarging, known low-grade glioma. On follow-up imaging for surgical planning of the low-grade glioma, a new area of concern was detected of a leptomeningeal-based lesion over the left frontal lobe. A biopsy of the frontal lobe lesion subsequently showed a primary intracranial sarcoma with DICER1 mutations, DICER1 p.Q1552 and p.D1709G. An important histology finding was that of prominent eosinophilic cytoplasmic globules, which are associated with intracranial sarcomas with DICER1 mutations. Additional molecular findings of this tumor included NF1 p.K1986fs and TP53 p.G279E mutations in the setting of this patient’s known history of NF1. A DICER mutation was not detected in the concurrent low-grade glioma at the time of his intracranial sarcoma diagnosis, thus thought not to be a germline-derived mutation. He went on to have a surgical resection with subsequent photon radiation therapy followed by consolidation chemotherapy. A Ewing sarcoma based regimen as per COG protocol AEWS1031 was selected for his therapy consisting of vincristine, doxorubicin, cyclophosphamide alternating with ifosfamide, etoposide (VDC-IE). This was chosen based on prior cases showing response to anthracycline-based regimens. This patient has overall shown improvement without signs of progression now 7 months out from his initial diagnosis. This case highlights the importance of recognizing the association of patients with NF1 being at an increased risk for the development of intracranial sarcomas with DICER1 mutations and correlation with histologic findings of eosinophilic cytoplasmic globules. It also points to the need for reporting these rare cases for optimization of therapy selection to provide a more standardized and evidence-based approach in the care for these patients.

RBIO-07. IMMUNOMODULATORY PATHWAYS MEDIATE RADIOTHERAPY RESPONSE IN MALIGNANT PERIPHERAL NERVE SHEATH TUMORS

Abstract PURPOSE Malignant peripheral nerve sheath tumors (MPNSTs) are the most common cause of death in neurofibromatosis type 1 (NF-1) and are resistant to radiation therapy (RT), yet the mechanisms underlying RT response are poorly understood. Here, we elucidate mechanisms of RT response in NF-1 associated peripheral nerve sheath tumors through genome-wide CRISPRi screens, genomic analysis of mouse models, and molecular analysis of patient-derived tumor specimens. METHODS Patient derived NF1 mutant plexiform neurofibroma (pNF) cells (NF9511b, NF95.6), and MPNST cells (ST88-14; JH2-002) were used to measure RT responses by cell counts and flow cytometry. Genome-wide CRISPRi screens were used to identify functional modifiers of RT response in ST88-14 and JH2-002 MPNST cells. Nf1-/-; Tp53-/- mouse MPNSTs were subcutaneously implanted in immunocompetent C57/B6 mice, irradiated (2Gyx5), and dissociated for single-cell RNA sequencing (scRNA-seq) using 10x Genomics. Human MPNST tumor specimens (n=45) were analyzed with targeted DNA mutation sequencing and methylation arrays for cell type deconvolution. RESULTS Radiation single-dose response curves revealed MPNST cells (IC50 6.85Gy) were radioresistant compared to pNF cells (IC50 3.13Gy). Genome wide CRISPRi screens in ST88-14 and JH2-002 MPNST cells converged on cell cycle, DNA repair, and immunomodulatory gene sets mediating RT sensitivity. Irradiation of subcutaneous mouse Nf1-/-; Tp53-/- MPNSTs significantly decreased tumor growth (p=0.01, t-test). scRNA-seq of 32,763 cells from 4 irradiated and 3 unirradiated mouse Nf1-/-; Tp53-/- MPNSTs identified 8 tumor clusters and 7 non-tumor clusters. Irradiation demonstrated a pro-inflammatory effect with increased T-cell presence (5.8% versus 3.3%, p=0.04, t-test) and greater activation of immunostimulatory genes (Cxcl10, Stat1, Irf7) in T cells. In human MPNSTs, CDKN2A/B deletion (p=0.04, log-rank test) and decreased immune cell composition (p=0.03, log-rank test) were associated with significantly worse overall survival in response to RT. CONCLUSION MPNST RT responses may depend on immunomodulatory mechanisms that could be leveraged to improve clinical RT response.

NIMG-04. MASSIVE THORACIC MENINGOCELE IN A PATIENT WITH NF1

Abstract Thoracic meningoceles are uncommon but when seen are often associated with neurofibromatosis 1 (NF1). Here we present a unique case where a massive thoracic meningocele presented with chest pain in a patient with NF1. A 56-year-old female with a diagnosis of NF1 presented with pain in the entire chest wall. She described the pain as circumferential around the entire chest “like a barrel”. Cardiology evaluation (with echocardiography) revealed no pulmonary hypertension or other cardiac disorder. MR angiogram of the chest also revealed no intrathoracic vascular structural abnormality. Inflammatory myopathy was considered to explain the pain but electromyography was unremarkable as were creatine kinase and erythrocyte sedimentation rate. MRI of thoracic spine demonstrated a large thoracic meningocele involving the spinal canal from T5-T10 and extending into the left hemithorax with measurements of 11.5 x 6.1 x 12.5 cm. Imaging was also notable for leftward displacement of the spinal cord toward the meningocele starting at the T6 level and extending to the T9 level with kyphosis of the thoracic spine centered on the block vertebral bodies forming the T7-T8 levels. Significant posterior scalloping was evident from T6-T10 with attendant dural ectasia. Neurosurgical consultation recommended no intervention to correct the meningocele as plication carried a risk of producing a subarachnoid-pleural fistula from the meningocele into the pleural space of the thoracic cavity. This case adds to our understanding of how unique and diverse the presentations of NF1 can be, and of the surgical challenges posed by NF1-associated meningoceles.

INNV-13. OPHTHALMOLOGICAL COMPLICATIONS IN NF-1 PATIENTS RECEIVING MEK INHIBITORS: MD ANDERSON CANCER CENTER EXPERIENCE

Abstract BACKGROUND MEK inhibitors (MEKi) are a novel therapy for plexiform neurofibromas and optic gliomas in Neurofibromatosis type 1 (NF1). Potential ophthalmic complications are MEKi-induced retinopathy (MEKAR) requiring regular ophthalmologic assessments. We assess the importance of screening and ocular adverse events (OAE) in pediatric NF1 patients receiving MEKi. METHODS We reviewed 45 NF1 patients with baseline and follow-up examinations before and post MEKi treatment initiation. Evaluations included comprehensive eye examination, visual acuity, dilated fundoscopic examination, optical coherence tomography (OCT) of the macula and nerve fiber layer, and Humphrey visual field testing. RESULTS Twenty-six (62% male) of 45 patients were included. Median age at treatment was 15 (range 2-23) years. Plexiform neurofibromas were the most common indication for MEKi (n=22). Selumetinib was the most common MEKi (n=19, 77%), then trametinib (n=6, 23%), and mirdametinib (n=1, 4%). Only two patients had to switch to different MEKi. Patients were followed for a mean of 413-days after treatment initiation (range 103-1122 days) for an average of 3.85 ophthalmology exams per patient. No retinopathy was observed at each of the 3–6 month follow-ups. Around 15% of patients experienced dry eye symptoms with none requiring artificial tears for management. Seven patients had pre-existing optic neuropathy. No dose adjustments were needed due to OAEs. One patient’s visual acuity decreased temporarily but returned to baseline and the patient remains on MEKi. CONCLUSIONS Regular ophthalmologic assessments are crucial for NF1 patients undergoing MEKi treatment. Consensus guidelines on frequency of ophthalmologic screening during MEKi treatment are not well reported. In our cohort no patients had MEKAR at regular 3–6 month follow ups. In addition to baseline screening, future larger cohort studies are needed to confirm if decreasing the frequency of retinal exams is safe while on MEKi to inform future clinical screening guidelines for NF1 patients on MEKi.

CNSC-43. NEUROTRANSMITTER DEPENDENCY UNDERLIES TUMOR GROWTH IN HUMANIZED PEDIATRIC LOW-GRADE GLIOMA MODELS

Abstract Brain tumors arise in close association with neurons, suggesting that these non-neoplastic cells may be critical stromal drivers of brain tumor initiation and growth. Previously, we have shown that murine low-grade optic glioma formation and progression in the setting of Neurofibromatosis type 1 (NF1) is dictated by neurons and neuronal activity. In these studies, these neuronal dependencies reflected neuronal activity-driven enzymatic cleavage of a growth factor (neuroligin-3) from oligodendrocyte precursors cells (tumor initiation) or neuronal production of a paracrine factor to stimulate T cell support of optic glioma growth (tumor progression). Since neurons typically communicate with other neurons through neurotransmitters, we sought to explore the possibility that neurotransmitters operate to modulate low-grade glioma growth using humanized mouse models of pilocytic astrocytoma (PA). Leveraging single cell RNA sequencing of three independent sets of pediatric PAs, we identified neurotransmitter pathway enrichment in the tumor cells. This neurotransmitter pathway enrichment reflected aberrant expression of specific neurotransmitter receptors, which we confirmed in three independently generated PA tissue microarrays and in five distinct primary PA cell lines grown in vitro. Moreover, this aberrant neurotransmitter receptor expression established differential neurotransmitter PA growth dependencies in vitro. Importantly, interruption of neurotransmitter signaling in human PA xenografts attenuated tumor growth and ERK activation in Rag1-/- mice in vivo. Finally, we discovered crosstalk between neurotransmitter receptor and receptor tyrosine kinase signaling that revealed another target for therapeutic inhibition. Taken together, these findings elucidate a previously unknown neurotransmitter PA growth dependency amenable to therapeutic targeting.

QOL-06. OPTIMIZING NEUROFIBROMATOSIS CARE: A COMPREHENSIVE ECONOMIC EVALUATION OF A SPECIALIZED EXPERTISE CENTER’S IMPACT ON PATIENT OUTCOMES

Abstract Neurofibromatosis type 1 (NF1), NF2-related schwannomatosis (NF2) and other schwannomatoses represent a spectrum of genetic disorders characterized by the development of tumors on nerve tissues, profoundly impacting patients’ quality of life and posing complex challenges. Recognizing the imperative for comprehensive care delivery, we undertook to implement a Neurofibromatosis Expertise Center (CE) at the Centre hospitalier de l’Université de Montréal (CHUM), Quebec, Canada. Employing a robust analysis framework, we aimed to assess the economic viability of the CE by quantifying the Quality-Adjusted Life Years (QALYs) gained through centralized multidisciplinary neurofibromatosis care (cost-utility ratio = CAD/QALY gained). Leveraging data from validated questionnaires including the SF-6D, our preliminary analysis revealed significant enhancements in patients’ quality of life across diverse domains, including physical pain, visible cutaneous lesions, cognitive dysfunction, hearing loss, malignancies, psychiatric comorbidities, unemployment, physical disability, and social isolation. Notably, among the respondents (N = 115), patients receiving CE services reported a 12% increase in general health compared to a 25% decline among those without CE services. Moreover, 28% of CE patients reported improved overall health compared to 12% of those without CE services. Using the Work Productivity and Activity Impairment questionnaire (WPAI-GH), we found that cohorts followed in CE for ≥ 1 year (N = 45) experienced less work productivity losses compared to the most recent cohort (N = 32), which presented scores exceeding 6 on a 1-to-10 scale. We hypothesize that the establishment of the CE will yield profound improvements in patient health outcomes and alleviate financial strains on the Ministère de la Santé et des Services Sociaux du Québec (MSSS). Therefore, our next steps include discussing a strategy for funding application to the MSSS to ensure the accessibility of necessary care for patients. Continuing data collection and analysis will also provide a more comprehensive overview of patient characteristics and needs.

EXTH-62. FOCAL ADHESION KINASE (FAK) IN CHROMOSOME 8 GAIN-ASSOCIATED MALIGNANT PERIPHERAL NERVE SHEATH TUMORS (MPNST)

Abstract OBJECTIVES Malignant peripheral nerve sheath tumors (MPNST) are aggressive sarcomas often associated with Neurofibromatosis type 1 (NF1), a genetic syndrome driven by overactivation of the RAS pathway. MEK inhibitors (MEKi) target downstream components of the RAS pathway and have been approved for NF1 patients with plexiform neurofibromas (PN). However, MPNST often develop resistance to MEKi. Our lab recently discovered the critical role of chromosome 8 (Chr8) genes in MPNST. The Chr8 gene, protein tyrosine kinase 2 (PTK2), also known as focal adhesion kinase (FAK) is overexpressed in multiple cancers, suggesting its importance in tumor progression. In this study, we aim to evaluate FAK as a therapeutic target for MPNST and investigate the FAKi and RAF/MEKi combination. METHODS A CRISPR gRNA screen was used to identify Chr8 genes involved in MPNST survival. The effect of FAK shRNA knockdown and a FAK inhibitor (FAKi), alone or combined with a MEKi, in MPNST cells was assessed using IncuCyte proliferation assays and multiple murine models. RESULTS The CRISPR gRNA screen identified 57 genes on Chr8 important for MPNST cell survival, including PTK2/FAK. Knockdown of FAK by shRNA in MPNST inhibited cell proliferation in vitro and reduced tumorigenesis in vivo. Consistently, the FAKi defactinib significantly inhibited the proliferation of MPNST (IC50-values: 1.72-4.65μM). Moreover, the defactinib/avutometinib combination was synergistic in vitro and the combination of FAKi with RAF/MEKi reduced tumor growth more that either drug alone in Chr8-gain MPNST PDX models. Avutometinib induced compensatory activation of FAK, while defactinib/avutometinib combination decreased phosphorylation of FAK, ERK1/2 and STAT3, and augmented cleavage of Caspase-3 and PARP-1, shown using the WES protein simple system. CONCLUSION These results demonstrate the potential therapeutic efficacy of FAK inhibitors, both alone and in combination with RAF/MEKi, for the treatment of MPNST.