However, Chi-square test revealed that cluster 2 patients were significantly associated with primary tumors (58%, P < 0.001), GBM histology (64%, P < 0.001), high-grade (64%, P < 0.001), elderly at diagnosis (62%, P < 0.001), IDH wild type (73%, P < 0.001), 1p/19q non-codeletion (97%, P < 0.001), and MGMT promoter un-methylation (49%, P = 0.009). This evidence concerns the gene IDH2 and glioblastoma.