Stéphanie Puget

Reduced H3K27me3 and DNA Hypomethylation Are Major Drivers of Gene Expression in K27M Mutant Pediatric High-Grade Gliomas

Two recurrent mutations, K27M and G34R/V, within histone variant H3.3 were recently identified in ∼50% of pHGGs. Both mutations define clinically and biologically distinct subgroups of pHGGs. Here, we provide further insight about the dominant-negative effect of K27M mutant H3.3, leading to a global reduction of the repressive histone mark H3K27me3. We demonstrate that this is caused by aberrant recruitment of the PRC2 complex to K27M mutant H3.3 and enzymatic inhibition of the H3K27me3-establishing methyltransferase EZH2. By performing chromatin immunoprecipitation followed by next-generation sequencing and whole-genome bisulfite sequencing in primary pHGGs, we show that reduced H3K27me3 levels and DNA hypomethylation act in concert to activate gene expression in K27M mutant pHGGs.

Recurrent activating ACVR1 mutations in diffuse intrinsic pontine glioma.

Diffuse intrinsic pontine gliomas (DIPGs) are highly infiltrative malignant glial neoplasms of the ventral pons that, due to their location within the brain, are unsuitable for surgical resection and consequently have a universally dismal clinical outcome. The median survival time is 9–12 months, with neither chemotherapeutic nor targeted agents showing substantial survival benefit in clinical trials in children with these tumors. We report the identification of recurrent activating mutations in the ACVR1 gene, which encodes a type I activin receptor serine/threonine kinase, in 21% of DIPG samples. Strikingly, these somatic mutations (encoding p.Arg206His, p.Arg258Gly, p.Gly328Glu, p.Gly328Val, p.Gly328Trp and p.Gly356Asp substitutions) have not been reported previously in cancer but are identical to mutations found in the germ line of individuals with the congenital childhood developmental disorder fibrodysplasia ossificans progressiva (FOP) and have been shown to constitutively activate the BMP–TGF-β signaling pathway. These mutations represent new targets for therapeutic intervention in this otherwise incurable disease.

Stereotactic biopsy of diffuse pontine lesions in children

OBJECT Empirical radiotherapy is the current treatment for children with diffuse pontine lesions that have imaging characteristics of an infiltrative malignant astrocytoma. The use of chemotherapeutic agents is, however, currently under investigation in the treatment of these tumors. To be included into a trial, patients need a definitive histological diagnosis. The authors present their prospective study of the stereotactic biopsy of these lesions during a 4-year period. METHODS A suboccipital, transcerebellar approach was used to obtain biopsy samples in 24 children. RESULTS Two patients suffered deficits. Both had a transient (< 2 months) new cranial nerve palsy; one of these patients also experienced an exacerbation of a preoperative hemiparesis. No patient died during the perioperative period. A histological diagnosis was made in all 24 patients as follows: 22 had a malignant infiltrative astrocytoma, one had a low-grade astrocytoma, and one had a pilocytic astrocytoma. The diagnosis of the latter two patients affected the initial treatment after the biopsy. CONCLUSIONS The findings of this study imply that stereotactic biopsy sampling of a diffuse pontine tumor is a safe procedure, is associated with minimal morbidity, and has a high diagnostic yield. A nonmalignant tumor was identified in two of the 24 patients in whom the imaging findings were characteristic of a malignant infiltrative astrocytoma. With the advent of new treatment protocols, stereotactic biopsy sampling, which would allow specific tumor characterization of diffuse pontine lesions, may become standard.

Beta-catenin status in paediatric medulloblastomas: correlation of immunohistochemical expression with mutational status, genetic profiles, and clinical characteristics†

Medulloblastoma is the most frequent malignant paediatric brain tumour. The activation of the Wnt/β‐catenin pathway occurs in 10‐15% of medulloblastomas and has been recently described as a marker for favourable patient outcome. We report a series of 72 paediatric medulloblastomas evaluated for β‐catenin protein expression, CTNNB1 mutations, and comparative genomic hybridization. Gene expression profiles were also available in a subset of 40 cases. Immunostaining of β‐catenin showed extensive nuclear staining (>50% of the tumour cells) in six cases and focal nuclear staining (<10% of cells) in three cases. The other cases either exhibited a signal strictly limited to the cytoplasm (58 cases) or were negative (five cases). CTNNB1 mutations were detected in all β‐catenin extensively nucleopositive cases. The expression profiles of these cases documented strong activation of the Wnt/β‐catenin pathway. Remarkably, five out of these six tumours showed a complete loss of chromosome 6. In contrast, cases with focal nuclear β‐catenin staining, as well as tumours with negative or cytoplasmic staining, never demonstrated CTNNB1 mutation, Wnt/β‐catenin pathway activation or chromosome 6 loss. Patients with extensive nuclear staining were significantly older at diagnosis and were in continuous complete remission after a mean follow‐up of 75.7 months (range 27.5–121.2 months) from diagnosis. All three patients with focal nuclear staining of β‐catenin died within 36 months from diagnosis. Altogether, these data confirm and extend previous observations that CTNNB1‐mutated tumours represent a distinct molecular subgroup of medulloblastomas with favourable outcome, indicating that therapy de‐escalation should be considered. International consensus on the definition criteria of this distinct medulloblastoma subgroup should be achieved. Copyright

Mesenchymal Transition and PDGFRA Amplification/Mutation Are Key Distinct Oncogenic Events in Pediatric Diffuse Intrinsic Pontine Gliomas

Diffuse intrinsic pontine glioma (DIPG) is one of the most frequent malignant pediatric brain tumor and its prognosis is universaly fatal. No significant improvement has been made in last thirty years over the standard treatment with radiotherapy. To address the paucity of understanding of DIPGs, we have carried out integrated molecular profiling of a large series of samples obtained with stereotactic biopsy at diagnosis. While chromosomal imbalances did not distinguish DIPG and supratentorial tumors on CGHarrays, gene expression profiling revealed clear differences between them, with brainstem gliomas resembling midline/thalamic tumours, indicating a closely-related origin. Two distinct subgroups of DIPG were identified. The first subgroup displayed mesenchymal and pro-angiogenic characteristics, with stem cell markers enrichment consistent with the possibility to grow tumor stem cells from these biopsies. The other subgroup displayed oligodendroglial features, and appeared largely driven by PDGFRA, in particular through amplification and/or novel missense mutations in the extracellular domain. Patients in this later group had a significantly worse outcome with an hazard ratio for early deaths, ie before 10 months, 8 fold greater that the ones in the other subgroup (p = 0.041, Cox regression model). The worse outcome of patients with the oligodendroglial type of tumors was confirmed on a series of 55 paraffin-embedded biopsy samples at diagnosis (median OS of 7.73 versus 12.37 months, p = 0.045, log-rank test). Two distinct transcriptional subclasses of DIPG with specific genomic alterations can be defined at diagnosis by oligodendroglial differentiation or mesenchymal transition, respectively. Classifying these tumors by signal transduction pathway activation and by mutation in pathway member genes may be particularily valuable for the development of targeted therapies.

Embryonal tumor with abundant neuropil and true rosettes (ETANTR), ependymoblastoma, and medulloepithelioma share molecular similarity and comprise a single clinicopathological entity

Three histological variants are known within the family of embryonal rosette-forming neuroepithelial brain tumors. These include embryonal tumor with abundant neuropil and true rosettes (ETANTR), ependymoblastoma (EBL), and medulloepithelioma (MEPL). In this study, we performed a comprehensive clinical, pathological, and molecular analysis of 97 cases of these rare brain neoplasms, including genome-wide DNA methylation and copy number profiling of 41 tumors. We identified uniform molecular signatures in all tumors irrespective of histological patterns, indicating that ETANTR, EBL, and MEPL comprise a single biological entity. As such, future WHO classification schemes should consider lumping these variants into a single diagnostic category, such as embryonal tumor with multilayered rosettes (ETMR). We recommend combined LIN28A immunohistochemistry and FISH analysis of the 19q13.42 locus for molecular diagnosis of this tumor category. Recognition of this distinct pediatric brain tumor entity based on the fact that the three histological variants are molecularly and clinically uniform will help to distinguish ETMR from other embryonal CNS tumors and to better understand the biology of these highly aggressive and therapy-resistant pediatric CNS malignancies, possibly leading to alternate treatment strategies.

Craniopharyngioma: the pendulum of surgical management

BackgroundFor a long time, craniopharyngiomas have been considered surgically attractive tumours. The fact that they are rare, histologically benign, and located in a challenging (but considered accessible) area made them worthy surgical prizes.MethodsAs we have saved vision and “cured” many of these tumours, the insidious and devastating effects on quality of life for these children has become evident.DiscussionThe state-of-the-art in the surgical management of craniopharyngioma is now turning to multi-modality treatment strategies (combination surgery and radiotherapy) aiming to limit morbidity. Questions remain—what factors influence our surgical decision making? Do we understand the long-term effects of the radiotherapy now being employed? We review a series of craniopharyngiomas looking for variables that correlated with outcome as perceived in terms of quality of life and we review briefly the history of craniopharyngioma surgery and the relevant literature.

Critical oncogenic mutations in newly diagnosed pediatric diffuse intrinsic pontine glioma.

Diffuse intrinsic pontine gliomas (DIPG) can not be cured with current treatment modalities. Targeted therapy in this disease would benefit from advanced technologies detecting relevant drugable mutations. Twenty patients with classic newly diagnosed DIPG underwent stereotactic biopsies and were analyzed for the presence of 983 different mutations in 115 oncogenes and tumor‐suppressor genes using OncoMap, a mass spectrometric method of allele detection. Our results identified oncogenic mutations in TP53 (40%), PI3KCA (15%), and ATM/MPL (5%) while none were identified in a large number of other genes commonly mutated in malignant gliomas. The identification of oncogenic mutations in the PI3K pathway offers the potential of a therapeutic target at initial diagnosis in this devastating disease. Pediatr Blood Cancer 2012; 58: 489–491.

Injuries to Inferior Vermis and Dentate Nuclei Predict Poor Neurological and Neuropsychological Outcome in Children With Malignant Posterior Fossa Tumors

Children treated for a malignant posterior fossa tumor (PFT) are at risk of intellectual impairment. Its severity is not explained by age and radiotherapy alone. The current study was designed to define the correlations between the anatomical damage and the neurological/neuropsychological deficits in children with a malignant PFT.

Childhood Craniopharyngioma: Hypothalamus-Sparing Surgery Decreases the Risk of Obesity

CONTEXT Craniopharyngioma is a brain tumor whose high local recurrence rate has for a long time led to a preference for extensive surgery. Limited surgery minimizing hypothalamic damage may decrease the severe obesity rate at the expense of the need for radiotherapy to complete the treatment. OBJECTIVE We compared weight gain and local recurrence rates after extensive resection surgery (ERS) and hypothalamus-sparing surgery (HSS). DESIGN Our observational study compared a historical cohort managed with ERS between 1985 and 2002 to a prospective cohort managed with HSS between 2002 and 2010. SETTING The patients were treated in a pediatric teaching hospital in Paris, France. PATIENTS Thirty-seven boys and 23 girls were managed with ERS (median age, 8 years); 38 boys and 27 girls were managed with HSS (median age, 9.3 years). MAIN OUTCOME MEASURES Data were collected before and 6 months to 7 years after surgery. Body mass index (BMI) Z-score was used to assess obesity and the number of surgical procedures to assess local recurrence rate. RESULTS Mean BMI Z-score before surgery was comparable in the 2 cohorts (0.756 after ERS vs 0.747 after HSS; P = .528). At any time after surgery, mean BMI Z-score was significantly lower after HSS (eg, 1.889 SD vs 2.915 SD, P = .004 at 1 year). At last follow-up, the HSS cohort had a significantly lower prevalence of severe obesity (28% vs 54%, P < .05) and higher prevalence of normal BMI (38% vs 17%, P < .01). Mean number of surgical procedures was not significantly different in the 2 cohorts. CONCLUSIONS Hypothalamus-sparing surgery decreases the occurrence of severe obesity without increasing the local recurrence rate.