Gliomas are the most common central nervous system tumors demonstrating an extremely broad range of clinical behavior. Over last few decades the understanding of molecular genetic mechanisms of tumor initiation and progression increased significantly. Furthermore, the identification of prognostic and predictive biomarkers aids the development of personalized and risk-adapted therapeutic approaches. In this review, we summarize the molecular findings in pediatric gliomas, both low and high grade (LGG and HGG), focusing on recurrent somatic mutations. There are nucleotide substitutions in BRAF, H3F3A, Hist1H3B/С, IDH1/2 genes, BRAF and NTRK1/2/3 fusions, and CDKN2A/B copy-number aberrations, known to be clinically relevant in the prognosis defining or predicting the efficacy of targeted therapy. We also describe how these findings could pave the way towards the novel genetic classification and risk-group stratification for pediatric patients with glial tumors.
Background. High-grade gliomas are characterized by a wide range of genetic abnormalities. The heterogeneous genomic landscape of pediatric high-grade gliomas allows identifying distinct subgroups of the disease in children and young adults. Most importantly, these subgroups differ by clinical course and prognosis, as well as treatment response to standard therapy.Objective: to assess the profile of molecular genetic markers of high-grade gliomas in children.Materials and methods. In the current study, we examine the frequency of H3F3A, Hist1H3B, BRAF, IDH1 / 2 mutations, the copy number alterations of CDKN2A / 2B genes and the expression of ETV6‑NTRK3 fusion gene in a cohort of 53 pediatric high-grade gliomas.Results. Driver mutations and CDKN2A / 2B deletions were observed in 24 (45 %) and 15 (28 %) of 53 tumors, respectively. Overall, the studied high-grade gliomas harbored 41 genetic aberrations including 24 (58.5 %) somatic missense mutations, 1 (2.4 %) genetic variant of unknown clinical significance, 1 (2.4 %) oncogenic fusion gene and 15 (36.6 %) deletions of the tumor suppressor genes.Conclusion. These findings point to the importance of molecular profiling of tumors for the optimal clinical care and development of new approaches to treatment aimed at molecular targets for personalized anticancer therapies.
The main pathogenetic mechanism of the development of pediatric low grade gliomas (pLGGs) is genetic aberrations in BRAF gene. This study is supported by the Independent Ethics Committee and approved by the Academic Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology, and Immunology. We analyzed the clinical and molecular characteristics of 69 patients with LGGs. Molecular genetic testing for BRAF V600E mutation was performed by allele-specific real-time PCR and Sanger sequencing. BRAF V600E mutation was detected in 15 (21.7%) patients with LGG. The majority of BRAF-mutated cases of LGGs had the midline location: OPG – 7, subcortical ganglia – 1, brainstem – 2. The 2-year PFS was much worse in patients with BRAF V600E compared to patients without this mutation – 30% and 66.2%, respectively. The median time to progression for patients with BRAF V600E mutation was 9.5 months compared to 3.1 years for patients without indicated substitution. 5 patients with BRAF V600E-mutated LGGs who experienced progression after the conventional treatment, received targeted therapy (BRAF-inhibitor-3, BRAF + MEK inhibitors – 2) with good response (complete response – 2, partial response – 3). BRAF V600E mutation contributes to poor outcome in patients with LGGs Targeted therapy could be effective in this cohort of patients.
Активное внедрение высокопроизводительного секвенирования в клиническую практику требует общего подхода к интерпретации обнаруженных генетических вариантов, в частности, вариантов с соматическим статусом. В 2017 году Ассоциация молекулярной патологии США (AMP), Американская коллегия медицинской генетики и геномики (ACMG), Американское общество клинической онкологии (ASCO) и Коллегия американских патологов (CAP) опубликовали руководство по интерпретации соматических генетических вариантов и выдаче заключений по результатам высокопроизводительного секвенирования опухолевой ДНК. Данный обзор посвящен специфике применения руководства AMP/ACMG/ASCO/CAP для интерпретации результатов генетических исследований детских солидных опухолей. В статье приводятся критерии, на которых основана классификация соматических генетических вариантов, обсуждаются проблемы оценки клинической значимости генетических находок и приводятся примеры классификации генетических вариантов, выявленных в различных типах детских солидных опухолей. Active clinical implementation of high-throughput DNA sequencing requires a common approach to the interpretation of detected genetic variants, including variants with somatic status. In 2017, the United States Association of Molecular Pathology (AMP), the American College of Medical Genetics and Genomics (ACMG), the American Society of Clinical Oncology (ASCO), and the College of American Pathologists (CAP) published the guidelines for interpreting and reporting the somatic genetic variants in cancer identified using high-throughput sequencing analysis. This review focuses on the specific application of the AMP/ACMG/ASCO/CAP guidelines in the field of genetic research on paediatric solid tumors. In particular, the review provides the criteria for classification of somatic genetic variants, discusses the problems of evaluating the clinical significance of genetic findings in paediatric tumors, and provides examples of classification of genetic variants specific for certain types of childhood solid malignancies.
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