Towards elucidating the oncogenic properties of mutated IDH1/2, we analysed The Cancer Genome Atlas (TCGA) and deduced that mutations in IDH1/2 and PTEN (Phosphatase and TENsin homologue), an important tumour suppressor frequently disrupted in many cancers, display mutual exclusivity in low-grade glioma (P<0.00001; Fisher's exact test) and glioblastoma multiforme (P=0.005; Fisher's exact test; Fig. 1a). The gene discussed is IDH1; the disease is glioma.