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e14547 Background: Glioblastoma (GBM) is the most aggressive brain malignancy with a heterogeneity molecular profile and accounts for no more than 3-5% of Central Nervous System tumors in children. Despite its rarity, pediatric GBM pertain different molecular genetics, outcome and effectiveness to therapies and remains an equally lethal tumor in children. Identification of genetic alterations in GBM of childhood and adolescence is important to refine molecular classification, define prognosis and therapeutic strategies. We aimed to detect and investigate molecular changes with potential prognostic marker and therapeutic target in GBM, using next generation sequencing (NGS) strategy. Methods: We selected 41 GBM samples from patients treated at Pediatric Oncology Institute/GRAACC. NGS was performed to identified genetic alterations in tumor samples using Oncomine Childhood Cancer Research Assay (OCCRA) panel, specific genetic panel for childhood and adolescence neoplasms. Results: We selected 41 GBM samples and identified 33 mutated genes. The most commonly detected genetic alterations were involving TP53, PDGFRA, PIK3CA, NF1, MYC, MET and genes with histone-related functions, including H3F3A and ATRX. Mutations in H3F3A K28M, ATRX and TP53 were most recurrent. ATRX alterations, either nonsense substitution or frameshift deletion, were exclusively found in patients with H3F3A K28M mutations. TP53 loss-of-function was exclusive in 9 of 41 (22%) tumors. In 7 of 9 cases (78%) harboring both H3F3A and TP53 mutations, patients died due to disease progression . In these patients, H3F3A-TP53 mutation is suggested to be unfavorable prognostic factor. Copy number alterations were found in 30% of GBM cases and PDGFRA-amplifications were the most frequent. PDGFRA-amplification was exclusively found in patients with H3F3A K28M mutations and 75% of these patients did not survived longer than two years. Conclusions: Molecular profiling based on NGS genetic panel, specific for pediatric tumors, can provide information about potential prognostic biomarkers for GBM of childhood and adolescence. Thus, wider understanding about GBM biologic heterogeneity may lead to personalized therapeutic strategies for pediatric patients.

10535 Background: Osteosarcoma (OS) is the most common malignant bone tumor in children and adolescents. Glutathione S-transferase (GST) and Cytochrome P-450 (CYP) family genes are involved in almost all anticancer drugs metabolism. The polymorphisms in these genes are associated with anticancer drugs resistance and toxicity events. This study aims to investigate the genotype frequencies of GSTM1, GSTT1, GSTM3, CYP1A2, CYP2C9 and CYP3A5 genes in OS patients and the influence of these polymorphisms in their clinical outcome. Methods: We investigated the peripheral blood DNA of 70 OS patients (25 metastatic and 45 nonmetastatic at diagnosis), following the GLATO - Latin American Group of Osteosarcoma Treatment - 2006. GSTM1 and GSTT1 deletion polymorphisms were examined through a multiplex-PCR and the GSTM3 polymorphism of three base pair-deletion using PCR-RFLP method. CYP1A2, CYP2C9 and CYP3A5 single nucleotide polymorphisms (SNPs) were investigated through real time PCR using TaqMan probe. Results: We found that GSTM1 null genotype was correlated with relapse occurrence (p=0,031) in patients that received high doses of chemotherapy. The CYP1A2*F allele was associated with lung metastasis (p=0,032), lung relapse (p=0,018) and high grade of ototoxicity (p=0,039). The CYP3A5*3 allele was associated with high grade of hepatotoxicity (p=0,010). The presence of at least one GSTM3*B allele was associated with better overall survival (p=0,045). The presence of CYP3A5*3 homozygous genotype was associated with better overall survival (p=0,043) in metastatic patients at diagnosis. The genotype GSTM3*B/ GSTM1 present, GSTM3*B/ GSTT1 present and GSTM3*B/CYP3A5*3 in metastatic patients at diagnosis were associated with better survival (p=0,048; p=0,004; p=0,012, respectively). Conclusions: The findings of this study suggest that GST and CYP polymorphisms may have a role in treatment response and may be an important marker in the future to personalized therapy in OS. Furthermore, CYP1A2*F allele is correlated with risk of lung metastasis and GSTM3*B homozygous genotype in combination with GSTM1 present, GSTT1 present and CYP3A5*3 were associated with better survival.