scholarly journals LGG-08. TREATMENT OUTCOMES AND TOLERABILITY OF TRAMETINIB IN PROGRESSIVE CIRCUMSCRIBED LOW-GRADE GLIOMAS

2021 ◽  
Vol 23 (Supplement_1) ◽  
pp. i32-i33
Author(s):  
Emily Hanzlik ◽  
Bridget Archambault ◽  
Mays Dairi ◽  
Kristin Schroeder ◽  
Mallika Patel ◽  
...  
Keyword(s):  
Treatment Outcomes ◽  
Mapk Pathway ◽  
Low Grade Glioma ◽  
Low Grade ◽  
Dramatic Improvement ◽  
Optic Pathway ◽  
Low Grade Gliomas ◽  
Radiographic Response ◽  
Dermatologic Toxicity ◽  
Best Responses

Abstract Circumscribed low-grade gliomas comprise roughly one-third of pediatric CNS tumors. Most of these tumors are caused by activating mutations in the mitogen-activated protein kinase (MAPK) pathway. Drugs targeting the MAPK pathway are effective in other cancers and are being utilized in low-grade gliomas. We describe treatment outcomes and toxicities in a series of thirteen low-grade glioma patients treated with trametinib. We performed a retrospective chart review to evaluate response on T2/FLAIR MRI images per updated RANO criteria, visual outcomes, tolerability, and durability of response in progressive low-grade glioma patients treated with trametinib. Thirteen patients age 22 months to 34 years were included. Best radiographic response on therapy included 2/13 partial response, 3/13 minimal response, 5/13 stable disease, and 3/13 progressive disease. Diagnoses included pilocytic astrocytoma (n=6), desmoplastic infantile ganglioglioma (DIG; n=1), and low-grade glial neoplasms (n=2). Molecular drivers included BRAF:KIAA1549 fusion (n=3), V600E mutation (n=1), and somatic NF1 mutation (n=1). Three patients had germline NF1. In patients with partial or minimal response, best response was seen after longer durations of therapy; 4 of 5 best responses occurred after at least 12 months on therapy. Five patients completed prescribed therapy. Three patients remain stable off therapy at 6, 12, and 21 months; two patients recurred at 1 and 10 months off therapy. Skin manifestations were the predominant form of toxicity. This was more severe in older males, and symptoms improved with intermittent dosing. All patients with optic pathway tumors showed at least stable vision throughout treatment, with some patients having dramatic improvement. Trametinib is effective and well-tolerated in patients with low-grade glioma. Dermatologic toxicity can be mitigated by intermittent dosing. Best responses tended to occur later in therapy, sometimes after relatively stable MRIs. Patients with optic pathway lesions showed stable to improved vision even in the absence of significant radiographic response.

scholarly journals TMOD-23. A NOVEL BRAF V600E LOW-GRADE GLIOMA MOUSE MODEL HIGHLIGHTS EXOMIC AND TUMOR IMMUNE ALTERATIONS AND DIFFERING THERAPEUTIC RESPONSES IN LOW- AND HIGH-GRADE GLIOMAS

2020 ◽  
Vol 22 (Supplement_2) ◽  
pp. ii232-ii233
Author(s):  
Anne Marie Barrette ◽  
Lasse Meyer ◽  
Yoko Hirata ◽  
Stefan Grossauer ◽  
Edbert Lu ◽  
...  
Keyword(s):  
Mapk Pathway ◽  
Low Grade Glioma ◽  
Braf V600e ◽  
Common Mutation ◽  
Low Grade ◽  
High Grade ◽  
Checkpoint Inhibition ◽  
Immune Infiltrate ◽  
Low Grade Gliomas

Abstract Pediatric low-grade glioma (pLGG), the most common brain cancer in children, is difficult to treat especially at recurrence. The BRAF V600E mutation is the second most common mutation in pLGG, and in a high-risk group for progression is associated with deletion of the tumor suppressor CDKN2A. A better understanding of the factors contributing to progression, in particular the role of the immune infiltrate is needed, but studies have been hindered by the lack of low-grade glioma mouse models. We utilized transgenic mice with a cre-activatable (CA) allele of BRAF V600E to generate endogenous models for low-grade gliomas. We found that BRAF V600E expression cooperates with hemizygous CDKN2A deletion to induce low-grade gliomas, with tumors forming at a greater latency than by homozygous deletion. Cell line derivatives from low-grade lesions continue to grow slower upon orthotopic injection than those we previously derived from high-grade tumors. Murine LGG can progress to higher grade tumors within the mouse lifespan and we observe exomic changes and alterations in the tumor immune infiltrate associated with progression, the details of which will be discussed at the meeting. High-grade cells’ phenotypic changes within in vivo passage are accompanied by exomic changes. The high-grade glioma immune infiltrate is altered by dual MAPK pathway inhibition with dabrafenib and trametinib. Adding dual immune checkpoint inhibition by anti-PD-L1 and anti-CTLA-4 antibodies significantly extends survival of dabrafenib-trametinib dual treatment. Human BRAF V600E mutant tumors reportedly have a higher tumor immune infiltrate than that of BRAF wildtype gliomas, consistent with our murine RESULTS: Here we present a novel model for BRAF V600E mutant gliomas in mice that has a frequent rate of progression, similar to human BRAF V600E mutant gliomas, and an active immune infiltrate in high grade tumors which makes them susceptible to the immunostimulatory effects of dual checkpoint inhibition.

scholarly journals LGG-18. EVEROLIMUS TREATMENT IN PEDIATRIC PATIENTS AFFECTED BY LOW-GRADE GLIOMAS (pLGG) NON-TSC, BRAF v600-WT

2020 ◽  
Vol 22 (Supplement_3) ◽  
pp. iii369-iii369
Author(s):  
Antonella Cacchione ◽  
Evelina Miele ◽  
Maria Chiara Lodi ◽  
Andrea Carai ◽  
Giovanna Stefania Colafati ◽  
...  
Keyword(s):  
Adverse Event ◽  
Disease Progression ◽  
Mapk Pathway ◽  
Brain Mri ◽  
Mammalian Target Of Rapamycin ◽  
Low Grade ◽  
Duration Of Treatment ◽  
Tumor Biopsy ◽  
Low Grade Gliomas ◽  
Personalized Approach

Abstract BACKGROUND MAPK pathway is the hallmark of pediatric low grade gliomas (pLGGs); hyperactivation of mTOR (mammalian target of rapamycin) might be a suitable biomarker for therapeutic response. We investigated the feasibility of Everolimus, mTOR inhibitor, in patients affected by pLGGs. METHODS Patients 1 to 18 years old, diagnosed with pLGG, with a positive tumor biopsy for mTOR/phospho-mTOR and radiological and / or clinical disease progression, treated at Bambino Gesù Children’s Hospital in Rome were evaluated. Tumor DNA methylation analysis was performed in 10 cases. Exclusion criteria included: Tuberous Sclerosis patients, Sub Ependymal Giant Astrocytoma. Everolimus was administered orally at a dose of 2.5 mg or 5 mg daily based on body weight. Patients were evaluated with brain MRI every 4, 8 and 12 months after treatment start and every six months thereafter. RESULTS 16 patients were enrolled from September 2014 and 2019. The median age was 7.5 years old. All patients had at least one adverse event. Events rated as severe (grade 3/4) were reported in 6 patients. Stomatitis was the most frequent adverse event. One patient discontinued treatment due to grade 4 toxicity (ulcerative stomatitis and fatigue). The median duration of treatment was 21 months (4–57 months). Brain MRI evaluations have showed disease stability in 11 patients, partial response in 2 patients and disease progression in 3 patients. CONCLUSIONS Everolimus has proven to be well tolerated and effective treatment in terms of disease stability in patients with pLGGs. It’s also an excellent example of chemo-free personalized approach.

scholarly journals LGG-50. INTEGRATED MOLECULAR AND CLINICAL ANALYSIS OF 1,000 PEDIATRIC LOW-GRADE GLIOMAS UNCOVERS NOVEL SUBGROUPS FOR CLINICAL RISK STRATIFICATION

2020 ◽  
Vol 22 (Supplement_3) ◽  
pp. iii375-iii376
Author(s):  
Uri Tabori ◽  
Scott Ryall ◽  
Michal Zapotocky ◽  
Julie Bennett ◽  
Liana Nobre ◽  
...  
Keyword(s):  
Risk Stratification ◽  
Clinical Presentation ◽  
Mapk Pathway ◽  
Clinical Analysis ◽  
Genetic Alterations ◽  
Low Grade ◽  
Who Grade ◽  
Low Grade Gliomas ◽  
Younger Age ◽  
Risk Categories

Abstract Pediatric low-grade gliomas (pLGG) are primarily driven by genetic alterations in the RAS/MAPK pathway, most commonly involving BRAF of NF1. Despite their molecular convergence, pLGG often show unexplained variability in their clinical outcome. To address this, we molecularly characterized a cohort of >1,000 clinically annotated pLGG. 84% of cases harbored a detectable driver mutation. The remaining 16% of patients nonetheless showed RAS/MAPK pathway up-regulation at the RNA level. The clinical presentation and outcome of pLGG appeared highly variable and linked to the alteration type: re-arrangement or SNV. Re-arrangement-driven tumors were diagnosed at a younger age (6.6 versus 10.9 years, p<0.0001), enriched for WHO grade I histology (88% versus 66%, p<0.0001), infrequently progressed (27% versus 46%, p<0.0001), and rarely resulted in death (3 versus 13%, p<0.0001) as compared to SNV-driven tumors. These included the rarest molecular drivers of pLGG, for which we now have the clinicopathologic features of including MYB, MYBL1, FGFR2 fusions, FGFR1-TACC1, FGFR1 SNVs, IDH1 p.R132H, and H3.3 p.K27M. Utilizing this information, we suggest novel risk categories of pLGG that effectively predicted patient outcome. Low-risk tumors progressed infrequently and rarely succumbed to their disease (10-year PFS of 71% and OS of 98%). Intermediate-risk pLGG had a 10-year PFS and OS of 35% and 90%, respectively. High risk pLGG almost invariably progressed (10-year PFS of 0%) and these patients often succumbed to their disease (10-year OS of 41%). These data highlight the biological and clinical differences between pLGG subtypes and offers molecular based risk stratification to these cancers.

scholarly journals Management of low-grade glioma: a systematic review and meta-analysis

2018 ◽  
Vol 6 (4) ◽  
pp. 249-258 ◽  
Author(s):  
Timothy J Brown ◽  
Daniela A Bota ◽  
Martin J van Den Bent ◽  
Paul D Brown ◽  
Elizabeth Maher ◽  
...  
Keyword(s):  
Systematic Review ◽  
Meta Analysis ◽  
Progression Free Survival ◽  
Low Grade Glioma ◽  
World Health ◽  
Subtotal Resection ◽  
Low Grade ◽  
Evidence Based ◽  
Free Survival ◽  
Low Grade Gliomas

Abstract Background Optimum management of low-grade gliomas remains controversial, and widespread practice variation exists. This evidence-based meta-analysis evaluates the association of extent of resection, radiation, and chemotherapy with mortality and progression-free survival at 2, 5, and 10 years in patients with low-grade glioma. Methods A quantitative systematic review was performed. Inclusion criteria included controlled trials of newly diagnosed low-grade (World Health Organization Grades I and II) gliomas in adults. Eligible studies were identified, assigned a level of evidence for every endpoint considered, and analyzed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The relative risk of mortality and of progression at 2, 5, and 10 years was calculated for patients undergoing resection (gross total, subtotal, or biopsy), radiation, or chemotherapy. Results Gross total resection was significantly associated with decreased mortality and likelihood of progression at all time points compared to subtotal resection. Early radiation was not associated with decreased mortality; however, progression-free survival was better at 5 years compared to patients receiving delayed or no radiation. Chemotherapy was associated with decreased mortality at 5 and 10 years in the high-quality literature. Progression-free survival was better at 5 and 10 years compared to patients who did not receive chemotherapy. In patients with isocitrate dehydrogenase 1 gene (IDH1) R132H mutations receiving chemotherapy, progression-free survival was better at 2 and 5 years than in patients with IDH1 wild-type gliomas. Conclusions Results from this review, the first to quantify differences in outcome associated with surgery, radiation, and chemotherapy in patients with low-grade gliomas, can be used to inform evidence-based management and future clinical trials.

scholarly journals ASSESSMENT OF THE EFFECT OF DIFFERENT PARAMETERS OF RADIOTHERAPY ON TREATMENT OUTCOMES OF INFILTRATIVE LOW-GRADE GLIOMA (GRADE II)

2017 ◽  
Vol 16 (4) ◽  
pp. 11-18
Author(s):  
V. A. Solodkiy ◽  
G. A. Panshin ◽  
N. V. Kharchenko ◽  
Z. S. Tsallagova ◽  
S. M. Milyukov ◽  
...  
Keyword(s):  
Treatment Outcomes ◽  
Low Grade Glioma ◽  
Low Grade ◽  
Grade Ii

Selumetinib in patients with tumors with MAPK pathway alterations: Results from Arm E of the NCI-COG pediatric MATCH trial.

2021 ◽  
Vol 39 (15_suppl) ◽  
pp. 10008-10008
Author(s):  
Carl E. Allen ◽  
Olive Eckstein ◽  
Paul M. Williams ◽  
Sinchita Roy-Chowdhuri ◽  
David R Patton ◽  
...  
Keyword(s):  
Clinical Trial ◽  
Stable Disease ◽  
Thromboembolic Event ◽  
Mapk Pathway ◽  
Low Grade Glioma ◽  
Braf V600e ◽  
Low Grade ◽  
Match Trial ◽  
Hotspot Mutations ◽  
Clinical Trial Information

10008 Background: The NCI-Children’s Oncology Group (COG) Pediatric Molecular Analysis for Therapy Choice (MATCH) trial assigns patients age 1 to 21 years with relapsed or refractory solid tumors, lymphomas, and histiocytic disorders to phase 2 treatment arms of molecularly-targeted therapies based on genetic alterations detected in their tumor. Arm E evaluated the MEK inhibitor selumetinib (ARRY-142886) in patients whose tumors harbored activating alterations in the MAPK pathway ( ARAF, BRAF, HRAS, KRAS, NRAS, MAP2K1, GNA11, GNAQ hotspot mutations; NF1 inactivating mutations; BRAF fusions). Methods: Patients received selumetinib 25 mg/m2/dose (max 75 mg/dose) PO BID for 28-day cycles until disease progression or intolerable toxicity with response assessments obtained every 2-3 cycles. The primary endpoint was objective response rate (ORR); secondary endpoints included progression-free survival (PFS). Patients with low grade glioma were excluded. Results: A total of 21 patients (median age 14 years; range 5-21) were enrolled between 10/2017 and 8/2019, with 20 patients evaluable for response. Diagnoses were high grade glioma (HGG; n = 8), rhabdomyosarcoma (n = 7), adenocarcinoma (n = 2), and one each of MPNST, endodermal sinus/yolk sac tumor, plexiform neurofibroma (PN), and neuroblastoma. MAPK pathway alterations detected consisted of inactivating NF1 mutations (n = 8), hotspot mutations in KRAS (n = 8), NRAS (n = 3), and HRAS (n = 1), and BRAF V600E (n = 2). No objective responses were observed. Three patients had a best response of stable disease (HGG with NF1 mutation, 6 cycles; HGG with KRAS mutation, 12 cycles; PN with NF1 mutation, 13 cycles prior to removal for dose-limiting toxicity). Six-month PFS was 15% (95% CI: 4%, 34%). Adverse events that were deemed possibly, probably, or definitely attributable to study drug included one case each of grade 3 uveitis, lymphopenia, and thromboembolic event; one grade 4 CPK elevation; and one grade 5 thromboembolic event. Conclusions: Selumetinib did not result in tumor regression in this cohort of children and young adults with treatment-refractory tumors with activating MAPK pathway alterations. Of note, two patients with HGG initially had stable disease, but ultimately progressed after 6 and 12 cycles, respectively. Selumetinib has previously demonstrated activity in low grade glioma and PN and is now FDA-approved for PN. The results of our study indicate that MAPK pathway mutation status alone is insufficient to predict response to selumetinib monotherapy. It is likely that selumetinib and other MEK inhibitors will require combination with targeted or cytotoxic agents for optimal efficacy in children with persistent or progressive cancers after front-line chemotherapy. Clinical trial information: NCT03213691. Clinical trial information: NCT03155620.

A phase II prospective study of selumetinib in children with recurrent or refractory low-grade glioma (LGG): A Pediatric Brain Tumor Consortium (PBTC) study.

2017 ◽  
Vol 35 (15_suppl) ◽  
pp. 10504-10504 ◽  
Author(s):  
Jason R. Fangusaro ◽  
Arzu Onar-Thomas ◽  
Tina Young-Poussaint ◽  
Shengjie Wu ◽  
Azra H Ligon ◽  
...  
Keyword(s):  
Phase Ii ◽  
Pediatric Brain Tumor ◽  
Braf V600e Mutation ◽  
Low Grade Glioma ◽  
Braf V600e ◽  
Low Grade ◽  
Optic Pathway ◽  
Grade 3 ◽  
Molecular Aberrations

10504 Background: A greater understanding of the Ras-MAP kinase-signaling pathway in pediatric low-grade glioma (LGG) paired with the availability of potent selective inhibitors has enhanced the ability to target this pathway with therapeutic intent. Methods: The PBTC conducted a multi-institutional phase II study (NCT01089101) evaluating selumetinib (AZD6244, ARRY-142886), a MEK I/II inhibitor, in children with recurrent/refractory LGG assigned to 6 strata and treated at 25 mg/m2/dose PO BID for up to two years. Here we present the data from three of these strata. The remaining strata are still accruing patients. Results: Stratum I included children with non-NF-1 and non-optic pathway recurrent/refractory pilocytic astrocytoma (PA) harboring BRAF aberrations (BRAF V600e mutation or the BRAF-KIAA 1549 fusion). Eight of 25 (32%) patients achieved a partial response (PR) with 2-year PFS of 66+/-11%. Two of 7 (29%) patient tumors with a BRAF V600e mutation and 6/18 (33%) with a BRAF KIAA-1549 fusion had a PR. Stratum 3 enrolled NF-1-associated LGG. Tissue for tumor BRAF evaluation was not required for eligibility. Ten of 25 (40%) achieved PR with a 2-year PFS of 96+/-4%. Only one patient progressed while on treatment. Stratum 4 included children with non-NF-1 optic pathway/hypothalamic LGG. Tissue for tumor BRAF evaluation was not required for eligibility. Two of 16 (12.5%) had a PR with a 2-year PFS of 65+/-13%. The BRAF aberration status of the responders in strata 3 and 4 is mostly unknown. All responses were confirmed centrally and seven patients remain on treatment. The most common toxicities were grade 1/2 CPK elevation, diarrhea, hypoalbuminemia, elevated AST and rash. Rare grade 3/4 toxicities included elevated CPK, rash, neutropenia, emesis and paronychia. Conclusions: Selumetinib was effective in treating children with recurrent/refractory LGG, including those with NF-1 associated LGG and PA harboring BRAF V600e mutation or BRAF-KIAA 1549 fusion. Larger prospective studies are necessary to determine the future, specific role of this agent in treating children with LGG harboring specific molecular aberrations. Clinical trial information: NCT01089101.

scholarly journals EPCT-16. LENALIDOMIDE ACTIVITY IN PILOCYTIC ASTROCYTOMA AND OPTIC PATHWAY GLIOMAS: REPORT ON CHILDREN’S ONCOLOGY GROUP ACNS1022

2021 ◽  
Vol 23 (Supplement_1) ◽  
pp. i50-i50
Author(s):  
Katherine Warren ◽  
Gilbert Vezina ◽  
Linda Springer ◽  
Allen Buxton ◽  
Cody Peer ◽  
...  
Keyword(s):  
Pilocytic Astrocytoma ◽  
Low Dose ◽  
Objective Response ◽  
Low Grade Glioma ◽  
Activity Level ◽  
High Dose ◽  
Low Grade ◽  
Optic Pathway ◽  
Long Term Effects ◽  
Optic Pathway Gliomas

Abstract Children with low-grade glioma have excellent survival rates but often suffer from the morbidity of treatment, particularly from cytotoxic chemotherapies. Targeted agents appear to have some activity but the long-term effects of inhibiting normal developmental pathways are unknown. Lenalidomide is an oral immunomodulatory agent with additional properties including anti-angiogenesis. Phase I studies indicated greater tolerability of this agent compared to adults, and a potential dose-response effect. We performed a Phase 2 trial of lenalidomide in children with pilocytic astrocytoma and optic pathway gliomas who failed initial therapy. The primary objective was to determine the objective response rate of children randomized to Regimen A low-dose (20 mg/m2 /dose) or Regimen B high-dose (115 mg/m2 /dose) lenalidomide, each administering lenalidomide daily x 21 days of each 28-day course. Secondary objectives included estimation of event-free survival (EFS) in this population and correlation of plasma lenalidomide concentration with toxicity and outcome. Results 74 eligible patients were enrolled (n=37 to each arm). The pre-defined activity level of interest was achieved for both arms. Objective responses were observed in both arms, with 4 partial responses in each. A total of n=18 patients completed 26 courses of therapy (Arm A, n=12, Arm B, n=6) The median number of courses on each arm was 14 (range 2–26) for Arm A and 11 for Arm B (range 1- 26). Of the 74 eligible patients who received study drug, 30 required a dose reduction for toxicity (Arm A, n=6, Arm B, n=24) and 16 discontinued treatment on protocol due to toxicity (Arm A, n=2, Arm B, n=14). Conclusion Lenalidomide demonstrates a sufficient level of activity in children with low-grade glioma to warrant further exploration in Phase 3 studies. Low-dose (20 mg/m2) lenalidomide appears to have better tolerability.

scholarly journals PDCT-15. EFFICACY AND SAFETY OF BEVACIZUMAB IN TREATING RECURRENT PEDIATRIC LOW-GRADE GLIOMA: A SYSTEMATIC REVIEW AND META-ANALYSIS OF PATIENT OUTCOMES

2019 ◽  
Vol 21 (Supplement_6) ◽  
pp. vi186-vi186
Author(s):  
Victor Lu ◽  
John Welby ◽  
David Daniels
Keyword(s):  
Adverse Events ◽  
Meta Analysis ◽  
Low Grade Glioma ◽  
Low Grade ◽  
Serious Adverse Events ◽  
Radiographic Response ◽  
Treatment Benefits ◽  
Rate Of Progression ◽  
Grade 3

Abstract BACKGROUND Although rare, the propensity for pediatric low-grade glioma (pLGG) to recur despite upfront intervention presents a management conundrum for clinicians. One novel salvage option is anti-angiogenic bevacizumab, however, its safety and efficacy in this specific demographic is poorly defined. Correspondingly, our aim was to pool systematically-identified metadata in the literature to substantiate the clinical relevance of bevacizumab in treating recurrent pLGG. METHODS Searches of 7 electronic databases from inception to June 2019 were conducted following PRISMA guidelines. Articles were screened against pre-specified criteria. The incidence of loss was then pooled by random-effects meta-analysis of proportions. RESULTS Six pertinent studies described the outcomes of 110 recurrent pLGG patients managed with bevacizumab. While on-treatment, the rate of clinical response was 58% (95% CI, 43–72%), and the rate of radiographic response was 80% (95% CI, 58–96%). Additionally, the rate of serious adverse events (Grade 3 and above) was 11% (95% CI, 5–18%), with proteinuria the most common of those events. By the time patients were off-treatment, the rate of progression was estimated to be 51% (95% CI, 28–74%). Certainty of these results ranged from very low to low. CONCLUSIONS The use of bevacizumab as therapy for recurrent pLGG appears to confer appreciable clinical and radiographic response with relatively low serious adverse events risk while on-treatment. However, the long-term off-treatment benefits of this therapy have yet to be consolidated. Traditional clinical heterogeneity concerns preclude the formalization of any recommendations until larger, more standardized investigations can be performed.

Novel RAF Fusions in Pediatric Low-Grade Gliomas Demonstrate MAPK Pathway Activation

2021 ◽  
Author(s):  
Katherine T Lind ◽  
Hannah V Chatwin ◽  
John DeSisto ◽  
Philip Coleman ◽  
Bridget Sanford ◽  
...  
Keyword(s):  
Mapk Pathway ◽  
Enrichment Analysis ◽  
Mitogen Activated Protein Kinase ◽  
Immunofluorescent Staining ◽  
Low Grade ◽  
Normal Brain ◽  
Mapk Activation ◽  
Low Grade Gliomas ◽  
Pathway Activation ◽  
Mitogen Activated Protein

Abstract Brain tumors are the most common solid tumor in children, and low-grade gliomas (LGGs) are the most common childhood brain tumor. Here, we report on 3 patients with LGG harboring previously unreported or rarely reported RAF fusions: FYCO1-RAF1, CTTNBP2-BRAF, and SLC44A1-BRAF. We hypothesized that these tumors would show molecular similarity to the canonical KIAA1549-BRAF fusion that is the most widely seen alteration in pilocytic astrocytoma (PA), the most common pediatric LGG variant, and that this similarity would include mitogen-activated protein kinase (MAPK) pathway activation. To test our hypothesis, we utilized immunofluorescent imaging and RNA-sequencing in normal brain, KIAA1549-BRAF-harboring tumors, and our 3 tumors with novel fusions. We performed immunofluorescent staining of ERK and phosphorylated ERK (p-ERK), identifying increased p-ERK expression in KIAA1549-BRAF fused PA and the novel fusion samples, indicative of MAPK pathway activation. Geneset enrichment analysis further confirmed upregulated downstream MAPK activation. These results suggest that MAPK activation is the oncogenic mechanism in noncanonical RAF fusion-driven LGG. Similarity in the oncogenic mechanism suggests that LGGs with noncanonical RAF fusions are likely to respond to MEK inhibitors.

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