The impact of methylome analysis on the diagnosis and treatment of CNS tumours in children and adolescents: A population-based study in Greece

The recently published WHO classification of central nervous system (CNS) tumours recognizes DNA methylation profiling as a desirable and, for some diagnoses, essential diagnostic tool adjunctive to conventional histopathology. DNA methylation profiling is not routinely available in many countries, including Greece. In this collaborative study, we report the DNA methylation results in a series of children and adolescents with CNS tumours in Greece (2018–2023). In total, 130 tumour samples were analyzed using the latest applicable version of the Heidelberg brain tumour classifier. Upon initial analysis, 80 % (104/130) achieved calibrated scores (Cs) ≥ 0.9 and matched an established methylation class family/subclass. Among them, methylation results confirmed (90/104, 86.5 %), refined (50/104, 48 %) or changed (10/104, 9.6 %) the histological diagnosis. Only four results were regarded as non-contributing (4/104, 3.9 %). Twenty-six tumour samples received Cs < 0.9. Despite low scores, methylation results supported the initial diagnosis with lower confidence in 38.5 % (10/26) and established the diagnosis in two tumours with non-conclusive histopathology. Additional t-distributed stochastic neighbour embedding (t-SNE) analysis allowed the possible classification of twelve tumours. Nine more samples reached high Cs using the newer brain tumour classifiers, since available. Samples co-tested in Greece demonstrated excellent test reproducibility, supporting the analysis' local implementation. Methylome profiling impacted the clinical management of 40 % of patients, modifying stratification, prognosis, or treatment approach. This study supports the need to integrate methylome analysis into routine diagnostics in our country and highlights the importance of collaboration between European pediatric oncology centres. •Methylation analysis increased diagnostic accuracy in pediatric CNS tumours.•In 40 % of patients, the clinical management was adapted based on the methylation results.•Local implementation of the analysis showed high test reproducibility.•Support integration of methylome analysis into routine diagnostics.•Importance of collaborative programs between paediatric oncology centres.