P01.46.B MOLECULAR ANALYSIS OF IDH MUTATED LOW GRADE GLIOMA PROGRESSION

Abstract BACKGROUND Isocitrate dehydrogenase-mutated (IDHmut) gliomas, frequently diagnosed at stage II, often recur at higher stages with increased aggressiveness. However, the molecular mechanisms driving these recurrences remain poorly understood, particularly given their highly variable timeline—occurring within months in some cases and years in others. This study aims to analyze the transcriptomes and methylomes of primary and recurrent tumors to identify patterns that could provide insight into the factors influencing tumor progression. MATERIAL AND METHODS To date, our study has included six astrocytomas (AC) and 24 oligodendrogliomas (ODG), all exhibiting at least one recurrence (19 patients). Among them, eight patients experienced two recurrences, while three had three recurrences. DNA and RNA were extracted from formalin-fixed, paraffin-embedded tumor sections marked by a pathologist to ensure a high tumor cell content (>70%). IDH status was determined using Sanger sequencing. RNA samples underwent transcriptome analysis using Clariom D microarrays, followed by processing with TAC 4.0 software for data analysis. Additionally, methylome profiling is currently being conducted using Illumina 935k methylation arrays, with findings to be presented at a later stage. RESULTS IDH mutation was detected in all primary tumor samples; however, in two ODG cases, the mutation was lost at the second recurrence. Differential gene expression analysis and unsupervised hierarchical clustering of all primary and recurrent samples identified four distinct clusters—two corresponding to primary tumors and two to recurrent cases. When analyzed by diagnosis, AC exhibited a clear separation between primary and recurrent tumors, with an increasing number of differentially expressed genes as recurrence progressed. Approximately 50% of differentially expressed genes were non-coding, with 3.46% belonging to miRNA precursors and 2.69% being small RNAs. In contrast, oligodendrogliomas showed no distinct differences in expression pattern when comparing primary and recurrent samples. CONCLUSION Transcriptome profiling revealed progressive alterations in recurrent AC cases, while ODG recurrence appears to follow a different trajectory. Further methylome analysis may offer deeper insights into the mechanisms driving glioma progression, and the inclusion of additional samples and treatment data could further enhance these findings.