P03.13 Evaluation of PIK3CA mutational status in glioma molecular subgroups

Abstract BACKGROUND Gliomas are the most common and lethal malignant tumors of central nervous system. In 2016, World Health Organization (WHO) classification included IDH mutations and 1p/19q codeletion as diagnostic criteria to define glioma entities. However, new biomarkers for diagnosis, prognosis and response to therapy are needed. In this context, PIK3CA mutations have been described as constitutive mutations, which highlights their relevance in gliomas. Here we clarified the clinical relevance of PIK3CA mutations according to the 2016 WHO classification, the potential impact on diagnosis, prognosis, response to therapy, as well as their correlation with EGFR amplification and PTEN deletion. MATERIAL AND METHODS A cohort of 444 adult diffuse glioma samples from Instituto Português de Oncologia Lisboa Francisco Gentil (IPOLFG) was classified according to the 2016 WHO Classification. The mutational status of exon 9 and 20 of PIK3CA was evaluated in molecular subgroups of gliomas by Sanger sequencing. PTEN deletion and EGFR amplification were identified by Fluorescent in situ hybridization (FISH). RESULTS PIK3CA mutations showed a higher frequency in the subgroup of gliomas with IDH mutations and 1p/19q codeletion - oligodendrogliomas (10%). In Glioblastoma (GBM) IDH-mutant and IDH-wildtype these oncogenic mutations were observed in 9% and 3% of cases, respectively. Similar results were obtained using The Cancer Genome Atlas (TCGA) data, which was 8% and 2%, respectively. H1047R and E542K were the most frequent mutations identified in the glioma molecular subgroups. Importantly, we found 3 unreported pathogenic variants in exon 20 of PIK3CA (c.3112T>C, c.2988T>C, c.3040C>T) and one polymorphic variant (c.3210A>G). In addition, PIK3CA mutations, PTEN deletion and EGFR amplification were not mutually exclusive alterations in glioma molecular subgroups. For the first time in gliomas, it was identified the rs45455192 polymorphism at a frequency of 16% in astrocytomas IDH-mutant, 24% in oligodendrogliomas and 18% in both molecular subgroups of GBM, although this polymorphism did not have prognostic value. The analysis of PIK3CA mutations in glioma recurrences showed that these mutations are maintained during glioma progression. CONCLUSION In two independent cohorts (IPOLFG and TCGA), it was obtained similar frequencies of PIK3CA mutations in GBM molecular subgroups. In addition, these mutations are more relevant in less aggressive gliomas (IDH-mutated and 1p/19q codeleted). These alterations seem to be important in tumor maintenance and progression, which makes this gene a potential therapeutic target. In the future, we will investigate the effect of the in vitro pharmacological inhibition of PIK3CA in GBM mutant cell lines.