IDH1 and glioblastoma: Co-gain of chromosomes 19 and 20, which has been described in a small series of long-term glioblastoma survivors [14], is frequently observed in the IDH-wildtype subgroup B. There is a significant survival difference (p = 0.034, Cox proportional hazards regression) between subgroups B and C, which are distinguished by gain of chromosome 19 (Additional file 1: Figure S1).