IDH1 and glioblastoma: Later work incorporating methylation data from a broader demographic, including pediatric patients led to the clustering of GBM into six categories including IDH, RTK-I (PDGFRA), RTK-II (Classic), Mesenchymal, K27, and G34. While the RTK-II and Mesenchymal groups were enriched for tumors within the Classical and Mesenchymal grouping from the Verhaak classification, the newer methylation data allowed for further subclassification of tumors that would have fallen within Verhaak’s Proneural group (7).