KIAA1549-BRAF Fusion Research Articles

Future perspective of targeted treatments in pediatric low-grade glioma (pLGG): the evolution of standard-of-care and challenges of a new era.

While surgery, when possible, remains the mainstay of pediatric low-grade glioma (pLGG) management, adjuvant therapy has significantly evolved over time. Radiation therapy was commonly used in the late 1990s for tumors that could not be resected or recurred. This resulted in significant late morbidity in this population and mortality related to secondary malignancies and chronic health conditions. Chemotherapy became the mainstay of adjuvant therapy but children still experienced late morbidity secondary to exposure to multiple lines of treatment over time. Targeted therapies emerged after the identification of frequent genetic alterations in the mitogen activated protein kinase (MAPK) pathway including KIAA1549-BRAF fusions and BRAF-V600 mutations and the near universal upregulation of the MAPK pathway in these tumors. Both BRAF and MEK inhibitors have shown efficacy in the treatment of pLGG and have led to prolonged stability in some cases. Multiple phase III clinical trials are now comparing targeted therapy to standard-of-care chemotherapy regimens setting the stage for targeted therapy to replace chemotherapy as the first-line treatment in some cases. Targeted therapy, however, is not without its challenges. There are clear examples of resistance and mechanisms of resistance have not been fully elucidated. There is also no clear duration for these therapies and rebound growth is a well-known phenomenon especially in BRAF-V600 mutant tumors. Targeted therapies are also fairly recent developments and long-term toxicities and functional outcomes are still being monitored. Very young and adolescent/young adult LGGs also carry molecular features that may not be addressed by inhibition of the MAPK pathway. Adjuvant therapy for pLGG has evolved from radiation for all unresectable or residual tumors to molecularly driven targeted therapies with improved quality of life, late effects, and less off-target toxicities. While there is still much to learn in regard to newer targeted therapies for pLGG, the era of targeted therapies for pediatric LGG is upon us.

OTHR-25. ANAPLASTIC TRANSFORMATION OF DIFFUSE LEPTOMENINGEAL GLIONEURONAL TUMORS: TWO PEDIATRIC CASES

Abstract BACKGROUND Diffuse Leptomeningeal Glioneuronal Tumors (DLGT) typically have a clinical course with slow progression; however, there have been cases of anaplastic transformation. We describe the clinical presentation, radiographic features, and molecular characteristics in 2 pediatric DLGT cases that underwent aggressive transformation. METHODS Patient 1: A 20 y/o male with DLGT with BRAF-KIAA1549 fusion and loss of 1p who was first diagnosed at 2.5 y/o. Over the course of 17 years, he was treated with numerous therapies due to multiple progressions, including temozolomide, carboplatin/vincristine, selumetinib, and vinblastine. At age 17, he developed significant growth of a posterior fossa mass with solid and cystic characteristics. Resection revealed new anaplastic pathologic features. Patient 2: He was diagnosed with DLGT at age 2 y/o. Imaging demonstrated intramedullary spinal nodules at T4 and T5 with abnormal thickening and enhancement over the cerebral leptomeningeal space. A biopsy revealed DLGT with a BRAF-KIAA1549 fusion, 1p loss and Ki67 5%. He received multiple therapies including carboplatin/vincristine, vinblastine, and selumetinib. RESULTS Patient 1: Molecular characterization revealed new ATRX mutation, and CDKN2A/B homozygous deletion. Over the following 2 years, he had multiple treatments, progressions, and surgeries. Final pathology revealed significant anaplasia with Ki67 90%, ATRX loss, and mutation of PPM1D and ARID1A. He rapidly declined. Patient 2: Approximately 2.5 years after diagnosis, he developed rapid progression in the 4th and lateral ventricles. Pathology confirmed recurrent DLGT, but with high-grade transformation, H3K27M (-), H3k27m3 loss, ATRX (+), Ki67 40%. He was treated with focal irradiation followed by temozolomide/CCNU. CONCLUSION In rare cases, DLGT can undergo anaplastic transformation. Once this occurs, it behaves clinically like a high-grade glioma. Understanding the molecular underpinnings and prognostic features that lead to this transformation are important for future study.

LGG-20. SELUMETINIB IN PEDIATRIC PATIENTS WITH RELAPSED/REFRACTORY OPTIC PATHWAY/HYPOTALAMIC LOW GRADE GLIOMA: A MONOINSTITUTIONAL EXPERIENCE

Abstract BACKGROUND Pediatric low-grade gliomas (pLGG) are the most common central nervous system tumors in children. The optic pathway and hypothalamic (OPH) frequent localizations are correlated with multiply relapses due to inoperability, thus emphasizing the need for alternative treatments. The results of activation of the BRAF oncogene through a tandem duplication resulting in a KIAA1549–BRAF fusion is the most common genetic aberration. Selumetinib is an oral mitogen-activated protein kinase (MEK) 1/2 inhibitor with promising efficacy and good tolerability on relapsed/refractory pLGG. METHODS From January 2021 to January 2024 three patients with refractory OPH-pLGG with KIIA1549-BRAF fusion were treated with Selumetinib 25 mg/sqm/day (compassionate use) all after two lines of chemotherapy. They were males, mean age at diagnosis 8 months, at starting Selumetinib 74 months. All had partial surgery at diagnosis and two of them other debulking surgeries during the treatment. All patients had numerous events of hydrocefalous with need of shunt revision. RESULTS Two patients experienced grade-3 stomatitis, one grade 3 nausea-vomiting, one grade 3 gastritis, one grade 1 increased level of CPK (CTCAE-V5.0). For grade 3 toxicity Selumetinib had to be stopped for a maximum of 7 days with clinical benefit. Two of them have completed treatment with Selumetinib, one is ongoing after 20 months, all with radiological stable disease at MRI. Median time of treatment is 26 months (range 20-30 months). All three experienced a trend in reduction of emergency room admission for ventricular-shunt problems. Median PFS at starting Selumetinib was 62 months, median OS is 97 months. CONCLUSIONS Selumetinib has a good profile of toxicity, allowing a good quality of life procrastinating radiotherapy and reducing surgery events in a context of heavily pretreated relapsed/refractory patients. Further data are needed on both visual and auxological parameters and late side effects.

LGG-21. IMMUNE MICROENVIRONMENT PROFILING OF BRAF-FUSION PILOCYTIC ASTROCYTOMA: DIRECTIONAL PRIORITIZATION OF IMMUNOTHERAPEUTIC TARGETS

Abstract BACKGROUND The immune microenvironment of pediatric gliomas is relatively understudied despite being a leading cause of childhood mortality. Pilocytic astrocytomas (PA) are the most common pediatric glioma and surgical resection is often curative. However, PAs are not always amenable to surgery and can have significant long-term morbidity and mortality. The ten-year progression-free survival for PA patients with significant residual tumor is less than 50% and other non-surgical treatment options are frequently necessary. METHODS To identify PA patients that may be responsive to immune checkpoint inhibitors and to guide prioritization of available immunotherapeutic treatments, orthogonal immune profiling strategies were used to identify patients that may benefit from the next generation of immune therapeutics. Because the KIAA1549-BRAF fusion is expressed in 70% of PA, we prospectively collected patients to comprehensively characterize the unique immune biology of these tumors using nanostring profiling, scRNASeq, and SeqIF™ multiplex staining. RESULTS The tumor microenvironment of BRAF-fusion PA was notable for antigen presentation and the interaction of CD11c+ cells with T cells through Lck+ immunological synapses. PA CD11c+CD206+ dendritic cells localized to vessel walls and were positive for TIM3 expression, an immune checkpoint marker. A unique highly activated microglia subcluster was identified that morphologically resembled T cells expressing TNF and TIM3. Our results are consistent with others that suggest potential benefit in targeting tumors with elevated MAPK activity. Finally, the expression of other immune checkpoints such as Lag-3, PD-1, and TIGIT are minimally co-expressed, suggesting that T cells are not in a state of exhaustion, as seen in adult high-grade gliomas. CONCLUSIONS Analysis of BRAF-fusion PA identified a unique highly activated P2RY12+ microglia population dispersed throughout the tumor microenvironment, active antigen presentation between a CD11c+ antigen presenting cells and T cells, and a unique therapeutic opportunity for targeting TIM3.

LGG-35. ROBUST TUMOR RESPONSE TO CHEMOTHERAPY IN THALAMIC PILOCYTIC ASTROCYTOMA WITH LARGE CYSTIC COMPONENT: A CASE REPORT

Abstract BACKGROUND Pilocytic astrocytoma (PA) is the most common glioma in children. Prognosis is excellent when complete resection is achievable. However, in central locations, such as optic pathway, thalamus, and brainstem, resection may lead to extensive morbidity, necessitating alternative treatment strategies. Chemo- and targeted therapy options have demonstrated efficacy in controlling tumor growth and providing clinical benefit; however, cystic portions are not typically responsive to either option. METHODS Case report, Retrospective chart review RESULTS A 4-year-old male presented with left sided weakness and ventriculomegaly. MRI of the brain revealed a 3.5 x 3.3 x 4.4 cm mixed solid and cystic enhancing mass extending from the right thalamus down to the right middle cerebellar peduncle. An endoscopic third ventriculostomy and tumor biopsy was performed. Histology confirmed PA, WHO Grade 1. Sequencing confirmed BRAF-KIAA1549 fusion. Chemotherapy was initiated with Carboplatin and Vincristine. Each subsequent MRI of the brain obtained during therapy and at the end of therapy demonstrated significant decrease in both solid and cystic portion of the tumor with complete resolution of symptoms and neurologic deficits. End of therapy MRI demonstrated 1.2 x 1.4 x 1.2 cm mixed solid and cystic mass. CONCLUSIONS The unique aspect of this case is the exceptional and robust response achieved in both solid and cystic components, challenging the historical notion of cystic lesions being less sensitive to chemotherapy. This observation can contribute valuable insights to the evolving understanding of treatment responses in these tumors.

LGG-05. REPORT ON PEDIATRIC BRAIN TUMOR CONSORTIUM (PBTC)-029B, A PROSPECTIVE PHASE 2 CLINICAL TRIAL OF SELUMETINIB IN TREATING YOUNG PATIENTS WITH RECURRENT/PROGRESSIVE LOW-GRADE GLIOMA: NEW RESULTS ON STRATA 2, 5, AND 6 WITH UPDATED LONG-TERM SURVIVAL OUTCOMES ON STRATA 1, 3, AND 4

Abstract BACKGROUND PBTC-029B was a phase 2 trial evaluating efficacy of selumetinib (up to 26 courses) in children with recurrent/progressive low-grade glioma. We report new results on strata 2, 5, and 6 as well as update long-term survival outcomes on strata 1, 3, and 4. METHODS Stratum 2 enrolled children with pilocytic astrocytoma (PA) whose tumor screened negative for the BRAF-KIAA1549 fusion and the BRAFV600E mutation. Stratum 5 enrolled children with non-PA whose tumor screened positive for one of these two BRAF aberrations. Stratum 6 enrolled children who consented to tissue screening, but there was an assay failure. Responses were based on T2/FLAIR. RESULTS Stratum 2: among 14 patients, there was 1 partial response (PR), 7 stable disease (SD) and 6 progressive disease (PD) with overall response rate (ORR) of 7.1%. Two-year progression-free survival (PFS)/overall survival (OS) were 57.1/100%, respectively. Stratum 5: among 23 patients, there was 1 complete response, 4 PR, 12 SD and 6 PD with ORR of 21.7%. Two-year PFS/OS were 74.8%/100%, respectively. Stratum 6: among 26 patients, there were 7 PR, 14 SD and 5 PD with ORR of 26.9%. Two-year PFS/OS were 72.0%/100%, respectively. Long-term outcomes have now been evaluated in strata 1, 3, and 4. Stratum 1 enrolled patients with PA whose tumor screened positive for one of the two BRAF aberrations; stratum 3 enrolled patients with neurofibromatosis type-1 (NF1) associated pLGG; and stratum 4 enrolled non-NF1 optic pathway/hypothalamic tumors. Among strata 1, 3, and 4, the current median follow-up for patients without events are 60.4, 60.4, and 58.1 months, respectively. Five-year PFS/OS are 30.8%/88.9%, 54.2%/100%, and 51.0%/100%, respectively. CONCLUSIONS These data demonstrate that selumetinib provides tumor stability and responses among diverse pLGG tumors as well as show that many patients will achieve long-term disease control even several years after stopping treatment.

LGG-24. PEDIATRIC GANGLIOGLIOMA WITH GERMLINE BRCA2 MUTATION

Abstract BACKGROUND BRCA1 and BRCA2 are genes associated with breast and ovarian cancer development in adults. Their influence on brain tumor formation is less understood. METHODS Retrospective review RESULTS An 11 year-old girl was diagnosed with ganglioglioma after presenting with seizures. Tumor sequencing revealed three mutations: a PDAP1-BRAF fusion, a BRAF-HIP1 non-canonical fusion, and a pathogenic BRCA2 variant D252*fs. Upon further review, a family history of breast cancer in the grandmother and several great-aunts was identified, and genetic testing confirmed this mutation to be germline. We then conducted an institutional review and identified a second pediatric low-grade glioma (pilocytic astrocytoma) patient with a pathogenic mutation in BRCA2 (T3085Fs*26) in addition to a BRAF-KIAA1549 fusion; the family declined germline BRCA2 testing. BRCA1/2 knockout models have demonstrated that both genes play a role in brain development. Concurrent BRCA2 and TP53 loss triggers formation of early onset murine medulloblastoma, a finding not observed with TP53 loss alone. In human patients, heterozygous and biallelic mutations in BRCA2 were identified as risk factors for medulloblastoma development in a recent integrative genomic analysis. Retrospective review CONCLUSION We report two cases of BRCA2 mutation in pediatric low-grade gliomas, one of which was confirmed to be germline. While somatic variants of BRCA2 have been reported in both high- and low-grade glioma, their role in these tumors has not been established to date. The BRCA2 tumor predisposition syndrome increases the risk of some types of brain tumors such as medulloblastoma, although the risk remains low compared to the risk of developing breast or ovarian cancer later in life. More evidence is required to determine whether BRCA2 germline mutations can similarly increase the risk of glioma formation.

Continuous response despite reduced dose of trametinib as single agent in an adolescent with a relapsed disseminated pediatric low-grade glioma KIAA1549-BRAF fusion positive: a case report and review of the literature

Dissemination in pediatric low-grade glioma may occur in about 4%–10% of patients according to retrospective cohort studies. Due to its low incidence, there is no consensus on treatment for these patients. According to the constitutional activation of the MAPK/ERK pathway in these tumors, MEK inhibitors such as trametinib have been used successfully in the relapsed setting. Skin toxicity is frequent in patients receiving trametinib, normally mild to moderate, but sometimes severe, needing to discontinue the drug, limiting the efficacy in the tumor. There is not much information in the literature regarding whether reducing the dose of trametinib is able to maintain efficacy while, at the same time, decreasing toxicity. Here, we present an adolescent, with severe skin toxicity, whose trametinib dose was reduced by 50% and efficacy on the tumor continued while skin toxicity significantly decreased.

Identification of Multiclass Pediatric Low-Grade Neuroepithelial Tumor Molecular Subtype with ADC MR Imaging and Machine Learning.

Molecular biomarker identification increasingly influences the treatment planning of pediatric low-grade neuroepithelial tumors (PLGNTs). We aimed to develop and validate a radiomics-based ADC signature predictive of the molecular status of PLGNTs. In this retrospective bi-institutional study, we searched the PACS for baseline brain MRIs from children with PLGNTs. Semiautomated tumor segmentation on ADC maps was performed using the semiautomated level tracing effect tool with 3D Slicer. Clinical variables, including age, sex, and tumor location, were collected from chart review. The molecular status of tumors was derived from biopsy. Multiclass random forests were used to predict the molecular status and fine-tuned using a grid search on the validation sets. Models were evaluated using independent and unseen test sets based on the combined data, and the area under the receiver operating characteristic curve (AUC) was calculated for the prediction of 3 classes: KIAA1549-BRAF fusion, BRAF V600E mutation, and non-BRAF cohorts. Experiments were repeated 100 times using different random data splits and model initializations to ensure reproducible results. Two hundred ninety-nine children from the first institution and 23 children from the second institution were included (53.6% male; mean, age 8.01 years; 51.8% supratentorial; 52.2% with KIAA1549-BRAF fusion). For the 3-class prediction using radiomics features only, the average test AUC was 0.74 (95% CI, 0.73-0.75), and using clinical features only, the average test AUC was 0.67 (95% CI, 0.66-0.68). The combination of both radiomics and clinical features improved the AUC to 0.77 (95% CI, 0.75-0.77). The diagnostic performance of the per-class test AUC was higher in identifying KIAA1549-BRAF fusion tumors among the other subgroups (AUC = 0.81 for the combined radiomics and clinical features versus 0.75 and 0.74 for BRAF V600E mutation and non-BRAF, respectively). ADC values of tumor segmentations have differentiative signals that can be used for training machine learning classifiers for molecular biomarker identification of PLGNTs. ADC-based pretherapeutic differentiation of the BRAF status of PLGNTs has the potential to avoid invasive tumor biopsy and enable earlier initiation of targeted therapy.

Abstract 5137: BRAF mutations in primary central nervous system tumors

Abstract Background: BRAF alterations are present in a variety of primary central nervous system (CNS) tumors from 3% in glioblastomas to 60% in pleomorphic xanthoastrocytomas. BRAF V600E mutation is the most common BRAF alteration found in tumors and has been successfully targeted by combining BRAF/MEK inhibitors in different tumor types, including gliomas. We aimed to describe the clinical and genomic features of primary CNS tumors harboring BRAF alterations and real-world data on BRAF-targeted therapy including our experience sequencing BRAF-directed therapies (BDI) in gliomas. Methods: Single-center retrospective analysis of patients with diagnosis of primary CNS tumors with NGS testing. Clinical, histological and molecular characteristics were analyzed. Results: 44 patients with BRAF mutant primary CNS tumors were included, 28 (64%) were male. 24 (55%) had histology consistent with high-grade glioma (HGG), 14 (32%) low grade glioma (LGG), 4 (9%) low grade neuroepithelial tumors and 2 (4%) others. Missense mutations were found in 77%, followed by amplifications (9%), fusions (9%) and in/del alterations (5%). V600E was the most common mutation (63%), followed by class 2 (16%) and 3 (7%) mutations and amplifications (9%). Co-occurring mutations were found in CDKN2A/B (22), TERT (20) and MTAP (12), median TMB was 2 mut/mb and only 2 patients had high TMB. 4 patients had commuted IDH1 (3 R132H), non-concurring with a V600E mutation. For patients with HGG, median age at diagnosis was 47 years and 16 (66%) were male. Lesions were more frequent in left hemisphere (70%) and temporal lobe (54%). V600E was found in 50% of cases, KIAA1549-BRAF fusion was found in 1 case. Median follow-up was 40 months (95% CI 11-68) and median overall survival (OS) was 22 months (3.4-40) for the whole population, and 56 (4-109) months for patients treated with BDI (n=4). All 4 patients had an OS >30 months. In the LGG cohort, median age at diagnosis was 34 years (IQR 24-46), 8 (57%) were male. 50% of the lesions were in the left side and 21% of the tumors were in the posterior fossa. 78% had a V600E mutation, with no statistical difference with HGG cohort (p=.082). Median follow up was 11 months, median OS was not reached. For 5 patients treated at recurrence with BDI, median PFS was 15 months (3-27).5 patients were treated with plixorafenib (PLX8394) on clinical trial achieving disease control (PR +SD) in 4 cases. Upon progression, 4 were rechallenged with dabrafenib + trametinib and 1 with another BDI. 4 patients had a partial response with duration of response >6 months in 3 cases. Conclusion: BRAF mutant CNS tumors are a heterogeneous disease. Longer survival was observed in the small group of HGG patients treated with BDI compared to SoC (56 months vs 22months). BDI rechallenge showed durable responses in heavily pretreated patients. Further molecular characterization of these patients is ongoing. The best therapeutical sequencing strategy for BDI remains uncertain. Citation Format: Juan B. Blaquier, Fulvio D'Angelo, Dalissa Tejera, Ruham A. Nasany, Gaurav Saigal, Antonio Iavarone, Macarena I. de la Fuente. BRAF mutations in primary central nervous system tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5137.

The potential of liquid biopsy for detection of the KIAA1549-BRAF fusion in circulating tumor DNA from children with pilocytic astrocytoma.

Low-grade gliomas (LGGs) represent children's most prevalent central nervous system tumor, necessitating molecular profiling to diagnose and determine the most suitable treatment. Developing highly sensitive screening techniques for liquid biopsy samples is particularly beneficial, as it enables the early detection and molecular characterization of tumors with minimally invasive samples. We examined CSF and plasma samples from patients with pilocytic astrocytoma (PA) using custom multiplexed droplet digital polymerase chain reaction (ddPCR) assays based on whole genome sequencing data. These assays included a screening test to analyze BRAF duplication and a targeted assay for the detection of patient-specific KIAA1549::BRAF fusion junction sequences or single nucleotide variants. Our findings revealed that 5 out of 13 individual cerebrospinal fluid (CSF) samples tested positive for circulating tumor DNA (ctDNA). Among these cases, 3 exhibited the KIAA1549::BRAF fusion, which was detected through copy number variation (CNV) analysis (n = 1) or a fusion-specific probe (n = 2), while 1 case each displayed the BRAF V600E mutation and the FGFR1 N577K mutation. Additionally, a quantitative analysis of cell-free DNA (cfDNA) concentrations in PA CSF samples showed that most cases had low cfDNA levels, below the limit of detection of our assay (<1.9ng). While CNV analysis of CSF samples from LGGs still has some limitations, it has the potential to serve as a valuable complementary tool. Furthermore, it can also be multiplexed with other aberrations, for example, to the BRAF V600 test, to provide important insights into the molecular characteristics of LGGs.

Treatment evaluation by volumetric segmentation in pediatric optic pathway glioma: evaluation of the effect of bevacizumab on intra-tumor components.

Progressive pediatric optic pathway gliomas (OPGs) are treated by diverse systemic antitumor modalities. Refined insights on the course of intra-tumoral components are limited. We performed an exploratory study on the longitudinal volumetric course of different (intra-)tumor components by manual segmentation of MRI at the start and after 3, 6 and 12months of bevacizumab (BVZ) treatment. Thirty-one patients were treated with BVZ (median 12months, range: 2-39months). During treatment the total tumor volume decreased with median 19.9% (range: -62.3 to + 29.7%; n = 30) within the first 3 months, decreased 19.0% (range: -68.8 to + 96.1%; n = 28) between start and 6 months and 27.2% (range: -73.4 to + 36.0%; n = 21) between start and 12months. Intra-tumoral cysts were present in 12 OPGs, all showed a decrease of volume during treatment. The relative contrast enhanced volume of NF1 associated OPG (n = 11) showed an significant reduction compared to OPG with a KIAA1549-BRAF fusion (p < 0.01). Three OPGs progressed during treatment, but were not preceded by an increase of relative contrast enhancement. Treatment with BVZ of progressive pediatric OPGs leads to a decrease of both total tumor volume and cystic volume for the majority of OPGs with emphasis on the first three months. NF1 and KIAA1549-BRAF fusion related OPGs showed a different (early) treatment effect regarding the tumor enhancing component on MRI, which did not correlate with tumor volume changes. Future research is necessary to further evaluate these findings and its relevance to clinical outcome parameters.

Pilocytic astrocytoma in adults: Histopathological, immunohistochemical and molecular study with clinical association

Pilocytic astrocytoma is the most common primary CNS neoplasm in children and adolescents, rare after the first two decades of life. While some authors report a favorable prognosis in the adult age group with the tumor, others have associated it with higher mortality. The molecular alteration most observed in cases of pilocytic astrocytoma in the pediatric group is the BRAF-KIAA1549 gene fusion, and there are still few studies confirming the presence of this fusion in the adult population. This work investigated genetic alterations involving the 7q34 region in BRAF gene in 21 adult individuals with pilocytic astrocytoma, by FISH. In addition, was identified the immunohistochemical expression of BRAFV600E, correlating these findings with histopathological and clinical ones. BRAF-KIAA1549 fusion appeared in only one case, while in two other cases were found deletions related to the FAM131B-BRAF fusion, suggesting that maybe the latter is more frequently in this population. Through the evaluation of immunoreactivity, 71% of the cases were considered positive and 29% negative. Cases considered positive for BRAFV600E immunoreactivity can potentially be treated through drug therapy with BRAF inhibitors; however, it is always recommended to carry out a molecular study for diagnostic confirmation. This is the first Brazilian study that aimed to investigate possible genetic alterations in the BRAF gene in pilocytic astrocytomas, specifically in adults. Only 1 patient died, but due to operative complications and not the disease itself, suggesting a good evolution of these individuals.

QLTI-01. HIGH-GRADE ASTROCYTOMA WITH PILOID FEATURES RESPONSE TO TREATMENT WITH CARBOPLATIN AND VINCRISTINE

Abstract High-grade astrocytoma with piloid features (HGAP) is a brain tumor that requires distinct DNA methylation profiling for diagnosis. The current literature on HGAP response to treatment is limited. This case details the response to treatment of a young female patient initially with a pilocytic astrocytoma that at progression transformed into HGAP, both diagnoses confirmed with methylation testing. At 12 years old, the patient initially presented with unremitting headaches and syncopal episodes. Imaging revealed a non-enhancing non-cystic lesion in the roof of the fourth ventricle measuring 5 mm in the greatest dimension. She was followed by serial surveillance until undergoing surgical resection four years later. Histologically the tumor was grade I pilocytic astrocytoma containing a KIAA1549-BRAF fusion; the diagnosis was subsequently confirmed with methylation array testing. The patient transitioned to serial surveillance until she was lost to follow-up. At 27 years old, she presented with progressive headaches, gait instability, and agraphia. MRI revealed a posterior fossa cerebellar mass and surgical resection was performed. Histologically this was an anaplastic pilocytic astrocytoma with KIAA1549-BRAF fusion; however, DNA methylation profiling confirmed the diagnosis of HGAP. The patient was treated with postoperative radiation and demonstrated asymptomatic tumor progression in the left cerebellar hemisphere fourteen months later. She received carboplatin and vincristine with radiographic response and stability for four months until discontinuation due to tumor progression with infiltrative disease within the posterior fossa and brainstem. Her treatment was transitioned to selumetinib with mixed radiographic response but continued clinical deterioration after three months. Selumetinib was terminated and best supportive care was initiated. The patient died 216 months from initial presentation with pilocytic astrocytoma and 28 months from transformation into HGAP. To our knowledge, this is the first report of HGAP with treatment response to carboplatin and vincristine. Further research into the best treatments for HGAP is needed.

CTNI-59. RARE AND NOVEL KIAA1549-BRAF FUSION BREAKPOINTS PREDICT POOR CLINICAL OUTCOME FOR PATIENTS WITH RECURRENT OR PROGRESSIVE PEDIATRIC LOW-GRADE GLIOMA: PHASE II PNOC001 TRIAL RESULTS

Abstract OBJECTIVES PNOC001 sought to estimate progression-free survival (PFS) associated with everolimus for progressive/recurrent pediatric low-grade glioma (pLGG) and to determine if activated PI3K/AKT/mTOR pathway as measured by positive phosphorylated-ribosomal protein S6 (p-RPS6) was associated with response. A secondary objective was to assess whether somatic drivers influence median PFS. METHODS Patients, 3-21 years of age, with recurrent/progressive pLGG received everolimus orally at 5 mg/m2 daily. Somatic drivers, when available, were associated with PFS and compared to four independent molecular pLGG cohorts with newly-diagnosed and progressive/recurrent patients. RESULTS From 2012 to 2019, 65 subjects enrolled [median age 9.6 years, 3.0-19.9; 46% female]; Median PFS for all-comers was 11.1 months (95%-CI 7.6-19.8, n = 64). PFS was not modulated by PI3K/AKT/mTOR pathway activation (median PFS 11.2 vs 9.4 months, P = 0.83, n = 62). BRAF alterations were identified in 67.8% (40/59) of patients. Rare/novel KIAA1549-BRAF fusion breakpoints were enriched in PNOC001 compared to newly-diagnosed pLGGs in independent cohorts (28.6% vs 2.6%, P = 1.4e-4, n = 214). In PNOC001, patients with rare/novel KIAA1549-BRAF fusion breakpoints had worse clinical outcomes than patients with common fusion breakpoints (median PFS 6.1 vs 16.7 months, P &amp;lt; 0.05, n = 20). Rare/novel KIAA1549-BRAF fusion breakpoints were also enriched in patients with progressive/recurrent disease in independent pLGG cohorts (17.6% vs 2.6%, P = 2e-3, n = 227). Integration of BRAF alterations and DNA methylation-based tumor subtypes further revealed that rare/novel KIAA1549-BRAF fusion breakpoints are more frequent in supratentorial midline (14.1%) compared to infratentorial (2.0%) pilocytic astrocytomas (P = 1e-4). KIAA1549-BRAF fusion breakpoints remained risk factors for progressive/recurrent disease in PNOC001 (P = 0.05) and independent pLGG cohorts (P &amp;lt; 0.05) after accounting for tumor location and DNA methylation subtypes. CONCLUSIONS Rare/novel KIAA1549-BRAF fusion breakpoints are more frequent in supratentorial midline pLGGs and define independent genomic risk factors for disease progression/recurrence. Our results indicate that future clinical trials must interrogate and define KIAA1549-BRAF fusion breakpoints for informative results and conclusions.

Use of bevacizumab in pediatric low-grade glioma: Ten-year experience in a single center

PurposePediatric low-grade gliomas (PLGG) have an excellent overall survival, but frequently need non-surgical therapy at diagnosis or after progression when located in unresectable sites such as the optic pathway. Chemotherapy side effects have led to the need for better-tolerated regimens with a sustained response. Bevacizumab, a humanized anti-VEGF monoclonal antibody has been used in monotherapy and/or in combination for these entities. Here we present our experience with its use in PLGG. MethodsThe authors performed a retrospective, observational, single-institution study, between 2008 and 2018, to evaluate the safety and efficacy of bevacizumab in progressive PLGG. ResultsTwenty-six patients with a median age at diagnosis of 3.32 years old [0.12–14.7] and a median age at treatment of 8.11 years old [0.41–16.82] were included in the study. Nineteen had optic pathway gliomas and chiasmatic-hypothalamic gliomas (73.1%), 9 of them (47.4%) associated with neurofibromatosis type 1 (NF1). Fourteen non-NF1 tumors were molecularly studied, disclosing BRAF-KIAA1549 fusion transcript in 9, and BRAF V600E mutation in 2. Bevacizumab was administered in combination with other agent(s) in 16 of the 35 treatment courses. Responses were assessed at 3, 12 months and at the end of treatment. Progression free survival at 12 and 36 months was 91.4% and 31.4%, respectively, and no severe adverse events were observed. ConclusionsIn our series, Bevacizumab in PLGG showed clinical efficacy with a favorable toxicity profile. Larger prospective studies may determine whether the response is conditional upon age, tumor location, and different histological and/or molecular characterization.

Radiomic features from multiparametric magnetic resonance imaging predict molecular subgroups of pediatric low-grade gliomas

BackgroundWe aimed to develop machine learning models for prediction of molecular subgroups (low-risk group and intermediate/high-risk group) and molecular marker (KIAA1549-BRAF fusion) of pediatric low-grade gliomas (PLGGs) based on radiomic features extracted from multiparametric MRI.Methods61 patients with PLGGs were included in this retrospective study, which were divided into a training set and an internal validation set at a ratio of 2:1 based on the molecular subgroups or the molecular marker. The patients were classified into low-risk and intermediate/high-risk groups, BRAF fusion positive and negative groups, respectively. We extracted 5929 radiomic features from multiparametric MRI. Thereafter, we removed redundant features, trained random forest models on the training set for predicting the molecular subgroups or the molecular marker, and validated their performance on the internal validation set. The performance of the prediction model was verified by 3-fold cross-validation.ResultsWe constructed the classification model differentiating low-risk PLGGs from intermediate/high-risk PLGGs using 4 relevant features, with an AUC of 0.833 and an accuracy of 76.2% in the internal validation set. In the prediction model for predicting KIAA1549-BRAF fusion using 4 relevant features, an AUC of 0.818 and an accuracy of 81.0% were achieved in the internal validation set.ConclusionsThe current study demonstrates that MRI radiomics is able to predict molecular subgroups of PLGGs and KIAA1549-BRAF fusion with satisfying sensitivity.Trial registrationThis study was retrospectively registered at clinicaltrials.gov (NCT04217018).

LGG-10. TREATMENT-RELATED MYELODYSPLASTIC SYNDROME FOLLOWING CHEMOTHERAPY FOR PEDIATRIC LOW-GRADE GLIOMA

Abstract Treatment-related myeloid neoplasms are rare though well-defined secondary malignancies associated with prior cytotoxic treatment, (particularly alkylating agents and topoisomerase inhibitors). They are rarely associated with primary central nervous system tumours and have historically carried a very poor prognosis. Pediatric low-grade gliomas (pLGG) are the most common CNS tumours of childhood, and up to 50% of patients will require adjuvant therapy. This has traditionally consisted of low-dose metronomic chemotherapy, although the advent of genomic profiling and identification of molecular drivers of pLGG means novel targeted therapies are changing this paradigm. There has only been a single reported case of treatment-related myeloid leukaemia secondary to pLGG treatment. We present a novel case of a 17-year-old girl with treatment-related myelodysplastic syndrome following chemotherapeutic treatment for pLGG. The patient was initially diagnosed at age 4 with a metastatic pilomyxoid astrocytoma (primary suprasellar lesion with spinal metastases) and received first-line treatment with a vincristine and carboplatin regimen. She had disease progression at age 7 and received second-line treatment with thioguanine, procarbazine, lomustine and vincristine. Following further progression at age 16, a biopsy of the suprasellar mass showed a pilocytic astrocytoma with a KIAA1549-BRAF fusion. Prior to commencing a targeted treatment as third-line therapy, she was noted to have a macrocytic anaemia, which subsequently evolved to a bicytopenia. Bone marrow analysis showed a hypocellular marrow with an abnormal myeloid clone with a chromosomal 1q gain, consistent with a diagnosis of treatment-related myelodysplastic syndrome. Germline analysis was negative for bone marrow failure predisposition gene abnormalities. She is currently undergoing workup for bone marrow transplant. Given the poor prognosis of treatment-related myeloid neoplasms, this case represents an important note of caution when choosing appropriate therapy for pLGG, especially given the evolving role for targeted treatments in this disease with otherwise very favourable long-term survival.

LGG-24. DIFFUSE LEPTOMENINGEAL GLIONEURONAL TUMOR MANAGEMENT AND OUTCOME: A SINGLE CENTER EXPERIENCE

Abstract Diffuse leptomeningeal glioneuronal tumor (DLGNT) is a rare diagnosis that was first incorporated into the WHO Classification in 2016. DLGNTs are usually low-grade tumors, with no current standard of care. A retrospective review of patients with a histologic diagnosis of DLGNT, from 2010 to 2022, was done with IRB approval. Eight patients were identified with a median age at diagnosis of 5.5 years (range 4 months - 21 years). Imaging findings included diffuse leptomeningeal enhancement and multifocal nodular lesions in the supratentorial and infratentorial locations. One patient had localized pineal disease and 2 patients had isolated spinal cord involvement. Histologically, 6/8 (75%) patients showed low-grade tumor (Ki-67 index = 2-15%). BRAF-KIAA1549 fusion was reported in 3, NTRK fusion in 1, PTPN11 mutation in 1, and FGFR1 mutation in 1 patient. Seven patients (88%) were treated with proton radiation, 3 at diagnosis and 4 upon progression. Chemotherapy was used at diagnosis on 4 patients (temozolomide, carboplatin and vincristine, and vinblastine). Targeted therapy (NTRK or BRAF-inhibitors) was utilized upon progression in four patients, and at diagnosis in one. All patients showed disease progression at a median time of 24 months from diagnosis. The median progression-free survival (PFS) in the group receiving upfront RT was 2.2 years (range = 0.4 – 6.6 years), versus chemotherapy of 1.4 years (range = 0.15 - 2.6 years) The 2 years PFS and OS are 57% and 100%, respectively. At a median follow-up of 4.5 years (range = 3 months to 9 years), 6 patients have stable disease (of whom 2 are off therapy), and 2 patients have progressive disease. DLGNTs are rare tumors with scarce data about radiological and molecular characteristics, and no established standard of care. Our case series emphasizes the need for further studies on molecular profiling and exploring targeted therapies.

Clinical activity of pan-RAF inhibitor tovorafenib in the registrational pediatric low-grade glioma arm of the phase 2 FIREFLY-1 (PNOC026) study.

10004 Background: Pediatric low-grade gliomas (LGGs) are the most common brain tumors of childhood. Genomic alterations of BRAF ( KIAA1549-BRAF fusions, 50–60% and BRAF V600E mutations, 5–15%) are the most frequent oncogenic drivers in pLGGs. Tovorafenib is an investigational, oral, selective, brain-penetrant, small molecule, type II pan-RAF inhibitor. Tovorafenib has demonstrated clinically meaningful responses in 24/35 patients (2 CR, 7 PR and 15 SD) in the pediatric phase 1B PNOC014 (NCT03429803) trial in patients with RAF-altered cancers (Wright, SNO 2022). Methods: FIREFLY-1 (NCT04775485) is a multicenter phase 2 study evaluating the efficacy and safety of tovorafenib monotherapy in patients with BRAF-altered cancers. Registrational arm 1 of FIREFLY-1 includes patients 6 months–25 years of age with recurrent or progressive LGG previously treated with ≥1 prior line of systemic therapy. Tovorafenib 420 mg/m2 (not to exceed 600 mg) is administered weekly, in 28-day cycles, (tablet or liquid suspension formulation) until progression. The primary endpoint of arm 1 is ORR, as defined by Response Assessment in Neuro-Oncology (RANO) criteria and determined by blinded independent review. Results: As of September 28, 2022, arm 1 had enrolled 77 patients and is fully accrued. All patients had ≥6 months of follow-up. Median age at enrollment was 8 years (range 2–21). Patients were pretreated with a median of 3 prior lines of systemic therapy (range: 1–9); 60% had received prior MAPK pathway-targeted agents. The most common tumor site was optic pathway (51%). Sixty-four patients harbored a BRAF fusion/rearrangement (83%) in their tumors, and 13 (17%) had a BRAF V600E mutation. Median duration of tovorafenib treatment is 8.4 months (range 0.7–16.8), with 59 patients (77%) remaining on treatment at the time of data cutoff. Per independent assessment in 69 RANO-evaluable patients, ORR was 64%, [3 CR, 41 PR (10 unconfirmed) and 19 SD] with a clinical benefit rate of 91%. Responses were achieved in tumors with BRAF fusions and V600E mutations, including those previously treated with MAPK inhibitors. The most common treatment-related adverse events (TRAEs) of any grade were hair color changes (75%), increased creatine phosphokinase (64%), anemia (46%), fatigue (42%) and maculopapular rash (42%). Tovorafenib dose modifications occurred in 16 (21%) and discontinuations in 2 (3%) patients due to TRAEs. Updates from a longer follow-up on the 77 patients in arm 1 will be presented at the meeting. Conclusions: Tovorafenib was generally well tolerated and showed encouraging evidence of antitumor activity in children and young adults with recurrent/progressive BRAF-altered pLGG. LOGGIC/FIREFLY-2 (NCT05566795), a global, phase 3 trial is evaluating once-weekly tovorafenib monotherapy in newly-diagnosed patients with pLGG harboring a known activating RAF alteration. Clinical trial information: NCT04775485 .