Ana Guerreiro Stucklin

BRAF Mutation and CDKN2A Deletion Define a Clinically Distinct Subgroup of Childhood Secondary High-Grade Glioma

PURPOSEnTo uncover the genetic events leading to transformation of pediatric low-grade glioma (PLGG) to secondary high-grade glioma (sHGG).nnnPATIENTS AND METHODSnWe retrospectively identified patients with sHGG from a population-based cohort of 886 patients with PLGG with long clinical follow-up. Exome sequencing and array CGH were performed on available samples followed by detailed genetic analysis of the entire sHGG cohort. Clinical and outcome data of genetically distinct subgroups were obtained.nnnRESULTSnsHGG was observed in 2.9% of PLGGs (26 of 886 patients). Patients with sHGG had a high frequency of nonsilent somatic mutations compared with patients with primary pediatric high-grade glioma (HGG; median, 25 mutations per exome; P = .0042). Alterations in chromatin-modifying genes and telomere-maintenance pathways were commonly observed, whereas no sHGG harbored the BRAF-KIAA1549 fusion. The most recurrent alterations were BRAF V600E and CDKN2A deletion in 39% and 57% of sHGGs, respectively. Importantly, all BRAF V600E and 80% of CDKN2A alterations could be traced back to their PLGG counterparts. BRAF V600E distinguished sHGG from primary HGG (P = .0023), whereas BRAF and CDKN2A alterations were less commonly observed in PLGG that did not transform (P < .001 and P < .001 respectively). PLGGs with BRAF mutations had longer latency to transformation than wild-type PLGG (median, 6.65 years [range, 3.5 to 20.3 years] v 1.59 years [range, 0.32 to 15.9 years], respectively; P = .0389). Furthermore, 5-year overall survival was 75% ± 15% and 29% ± 12% for children with BRAF mutant and wild-type tumors, respectively (P = .024).nnnCONCLUSIONnBRAF V600E mutations and CDKN2A deletions constitute a clinically distinct subtype of sHGG. The prolonged course to transformation for BRAF V600E PLGGs provides an opportunity for surgical interventions, surveillance, and targeted therapies to mitigate the outcome of sHGG.

Clinical and treatment factors determining long-term outcomes for adult survivors of childhood low-grade glioma: A population-based study.

The determinants of outcomes for adult survivors of pediatric low‐grade glioma (PLGG) are largely unknown.

Therapeutic and prognostic implications of BRAF V600E in pediatric low-grade gliomas

Purpose BRAF V600E is a potentially highly targetable mutation detected in a subset of pediatric low-grade gliomas (PLGGs). Its biologic and clinical effect within this diverse group of tumors remains unknown. Patients and Methods A combined clinical and genetic institutional study of patients with PLGGs with long-term follow-up was performed (N = 510). Clinical and treatment data of patients with BRAF V600E mutated PLGG (n = 99) were compared with a large international independent cohort of patients with BRAF V600E mutated-PLGG (n = 180). Results BRAF V600E mutation was detected in 69 of 405 patients (17%) with PLGG across a broad spectrum of histologies and sites, including midline locations, which are not often routinely biopsied in clinical practice. Patients with BRAF V600E PLGG exhibited poor outcomes after chemotherapy and radiation therapies that resulted in a 10-year progression-free survival of 27% (95% CI, 12.1% to 41.9%) and 60.2% (95% CI, 53.3% to 67.1%) for BRAF V600E and wild-type PLGG, respectively ( P < .001). Additional multivariable clinical and molecular stratification revealed that the extent of resection and CDKN2A deletion contributed independently to poor outcome in BRAF V600E PLGG. A similar independent role for CDKN2A and resection on outcome were observed in the independent cohort. Quantitative imaging analysis revealed progressive disease and a lack of response to conventional chemotherapy in most patients with BRAF V600E PLGG. Conclusion BRAF V600E PLGG constitutes a distinct entity with poor prognosis when treated with current adjuvant therapy.

Profound clinical and radiological response to BRAF inhibition in a 2-month-old diencephalic child with hypothalamic/chiasmatic glioma.

Infants with low‐grade glioma (LGG) have a poor survival. BRAFV600E mutation has been identified in pediatric LGG; however, the use of BRAF inhibitors in infants has never been reported. A 2‐month‐old with V600E mutant hypothalamic/chiasmatic glioma progressed on chemotherapy resulting in profound visual loss, massive ascites, and diencephalic syndrome. Initiation of dabrafenib resulted in rapid and sustained disappearance of clinical symptoms and a profound sustained cytoreduction. BRAF inhibition was safely tolerated with dramatic clinicoradiological response, suggesting early targeted therapy is a viable option in infants with LGG. A re‐evaluation of current management paradigms in this population is warranted to leverage the potential benefit of upfront‐targeted therapies.

The Changing Landscape of Pediatric Low-Grade Gliomas: Clinical Challenges and Emerging Therapies

Pediatric low-grade gliomas (PLGGs) are the most common brain tumors in children. Though histologically benign and associated with excellent outcome, patients with unresectable lesions--mostly young children with midline tumors--experience multiple progressions and are at increased risk for long-term neurological sequelae. PLGGs in children with underlying genetic predisposition syndromes--especially neurofibromatosis type 1 and tuberous sclerosis--have a distinct natural history and biology with important treatment implications. Given the complexity of medical issues, optimal management requires a large network of health care providers; treatment decisions must address both tumor control and potential side effects of the therapy. Current treatment strategies often fail to induce sustained tumor regression and many children require several lines of therapy, highlighting the need for novel therapies. Here, we review the current management of PLGG and discuss how new molecular targets--in particular alterations of the Ras/MAPK pathway--are rapidly changing our approach to PLGG.

Multiplex Detection of Pediatric Low-Grade Glioma Signature Fusion Transcripts and Duplications Using the NanoString nCounter System

Previous studies identified recurrent fusion and duplication events in pediatric low-grade glioma (pLGG). In addition to their role in diagnosis, the presence of these events aid in dictating therapy and predicting patient survival. Clinically, BRAF alterations are most commonly identified using fluorescent in situ hybridization (FISH). However, this method is costly, labor-intensive and does not identify nonBRAF events. Here, we evaluated the NanoString nCounter gene expression system for detecting 32 of the most commonly reported fusion/duplication events in pLGG. The assay was validated on 90 pLGG samples using FISH as the gold standard and showed sensitivity and specificity of 97% and 98%, respectively. We next profiled formalin-fixed paraffin-embedded preserved biopsy specimens from 429 pLGG cases. 171 (40%) of the cases within our cohort tested positive for a fusion or duplication event contained within our panel. These events, in order of prevalence, were KIAA1549-BRAF 16;9 (89/171, 52.0%), KIAA1549-BRAF 15;9 (42/171, 24.6%), KIAA1549-BRAF 16;11 (14/171, 8.2%), FGFR1-TACC1u200917;7 (13/171, 7.6%), MYBL1 duplication (5/171, 2.9%), KIAA1549-BRAF 18;10 (4/171, 2.3%), KIAA1549-BRAF 15;11 (2/171, 1.2%), FAM131B-BRAF 2;9 (1/171, 0.6%), and RNF130-BRAF 3;9 (1/171, 0.6%). This work introduces NanoString as a viable clinical replacement for the detection of fusion and duplication events in pLGG.

Tailoring Medulloblastoma Treatment Through Genomics: Making a Change, One Subgroup at a Time

After more than a decade of genomic studies in medulloblastoma, the time has come to capitalize on the knowledge gained and use it to directly improve patient care. Although metastatic and relapsed disease remain poorly understood, much has changed in how we define medulloblastoma, and it has become evident that with conventional therapies, specific groups of patients are currently under- or overtreated. In this review, we summarize the latest insights into medulloblastoma biology, focusing on how genomics is affecting patient stratification, informing preclinical studies of targeted therapies, and shaping the new generation of clinical trials.

Review of molecular classification and treatment implications of pediatric brain tumors

Purpose of review Brain tumors are the most common solid tumors and leading cause of cancer-related death in children. The advent of large-scale genomics has resulted in a plethora of profiling studies that have mapped the genetic and epigenetic landscapes of pediatric brain tumors, ringing in a new era of precision diagnostics and targeted therapies. In this review, we highlight the most recent findings, focusing on studies published after 2015, and discuss how new evidence is changing the care of children with brain tumors. Recent findings Genome-wide and epigenome-wide profiling data have revealed distinct tumor entities within, virtually, all pediatric brain tumor groups including medulloblastoma; ependymoma; high-grade and low-grade gliomas; atypical teratoid/rhabdoid tumors; and other embryonal tumors, previously called CNS primitive neuroectodermal tumors. Whenever integrated with clinical information, many molecular alterations emerge as powerful prognostic markers and should thus be used to stratify patients and tailor therapies. Summary Optimal integration of this newly emerging knowledge in a timely and meaningful way into clinical care is a remarkable task and a matter of active debate. The historical morphology-based classification of tumors is being replaced by a genetic-based classification, and the first generation of molecularly informed clinical trials is underway.

TGF-β Determines the Pro-migratory Potential of bFGF Signaling in Medulloblastoma

The microenvironment shapes cell behavior and determines metastatic outcomes of tumors. We addressed how microenvironmental cues control tumor cell invasion in pediatric medulloblastoma (MB). We show that bFGF promotes MB tumor cell invasion through FGF receptor (FGFR) inxa0vitro and that blockade of FGFR represses brain tissue infiltration inxa0vivo. TGF-β regulates pro-migratory bFGF function in a context-dependent manner. Under low bFGF, the non-canonical TGF-β pathway causes ROCK activation and cortical translocation of ERK1/2, which antagonizes FGFR signaling by inactivating FGFR substrate 2 (FRS2), and promotes a contractile, non-motile phenotype. Under high bFGF, negative-feedback regulation of FRS2 by bFGF-induced ERK1/2 causes repression of the FGFR pathway. Under these conditions, TGF-β counters inactivation of FRS2 and restores pro-migratory signaling. These findings pinpoint coincidence detection of bFGF and TGF-β signaling by FRS2 as a mechanism that controls tumor cell invasion. Thus, targeting FRS2 represents an emerging strategy to abrogate aberrant FGFR signaling.

LGG-18. MOLECULAR ALTERATIONS PREDICT RESPONSE TO CHEMOTHERAPY AND OUTCOME OF PEDIATRIC LOW-GRADE GLIOMA

Abstract BACKGROUND: Pediatric low-grade glioma (pLGG) is the most common childhood brain tumor. Recently, alterations of the RAS/MAPK pathway have been identified as the major driver of PLGG however little is known about prognostic implications. DESIGN/METHODS: We undertook a large population based study of all pLGG diagnosed from 1985–2015. Detection of known pLGG-related fusions was evaluated by NanoString and point mutations BRAF-V600E and H3.3K27M were evaluated using QX200™Droplet Digital™PCR. Results were correlated with outcome and response to chemotherapy. RESULTS: BRAF was found to be altered (KIAA1549-BRAF or BRAF-V600E) in 57% of patients in our pLGG cohort with full clinical and molecular data (n=480). Other alterations accounted for 6% of cases (FGFR1-TACC1(n=9), MYBL1(n=5), H3.3K27M(n=10)). The remaining 37% pLGG cases did not harbor any of evaluated alterations. Additional 134 patients with neurofibromatosis-1(NF1) were included in survival analysis. Kaplan-Meier analysis revealed 10-year PFS 72.3% for NF1, 68.3% for all KIAA1549-BRAF, and 28.4% for BRAF-V600E(p<0.0001). Among other alterations, H3.3K27M delineated a poor prognostic group with behavior similar to high-grade glioma. All patients with FGFR1-TACC1 and MYBL1 were alive at the time of analysis despite several observed progressions. Furthermore, we evaluated whether differences in survival could be correlated with response to conventional therapy in 92 patients. Change in tumor size at 6xa0months of chemotherapy differed depending on alteration. 45% of patients with BRAF-KIAA1549 responded to first line chemotherapy, and only 7.5% progressed. Similarly, 35% of NF1 patients responded and none progressed. In contrast, only 15% BRAF-V600E responded and more than half of tumors exhibited growth after six months of chemotherapy. CONCLUSIONS: In contrast to BRAF-V600E, KIAA1549-BRAF defines a group of pLGG patients with excellent prognosis and response to chemotherapy similar to NF1. Biopsy should be mandated in order to predict outcome, response to chemotherapy and evaluate targets for novel therapies.