DNA methylation analysis reveals an epigenetic signature distinctive of high-grade oligodendroglioma

IDH-mutant gliomas represent a subtype of diffuse gliomas that primarily affect patients in early to mid-adolescence. These tumors are classified into three distinct CNS WHO grades of malignancy. Accurate grading is essential for selecting an appropriate treatment maximizing anti-tumor efficacy while minimizing adverse effects. However, grading of oligodendrogliomas with 1p/19q codeletion currently relies on qualitative tumor characteristics that may be influenced by observer subjectivity, sampling bias, and tumor heterogeneity. This study aimed to explore DNA methylation-based tumor deconvolution into latent methylation components (LMCs) to evaluate their potential as objective grading tools in a cohort of 137 IDH-mutant gliomas. LMCs were analyzed in relation to malignancy markers, cellular composition, and underlying methylation signatures of the chromatin landscape. Glioma subtypes were associated with distinct LMCs. Two LMCs correlated with higher cellular density and advanced epigenetic age as well as with microvascular proliferation, necrosis, and epigenetically defined high-grade astrocytoma. The epigenetic patterns defining high-grade astrocytoma or oligodendroglioma, respectively, were similar. Higher-grade oligodendrogliomas, identified by LMC-based grading, were associated with more copy number alterations. Among patients of an external cohort who died during the assessment period, higher LMC1 proportions were associated with poorer overall survival. Therefore, LMCs hold the potential to support IDH-mutant glioma grading by incorporating objective epigenetic markers.