The combination of histological assessment with conventional molecular testing (i.e. IHC, targeted sequencing, copy number assay) is in our practice the first line diagnostic approach and is adequate for the majority of intrinsic tumours, such as IDH-mutant astrocytomas, oligodendrogliomas, histone-mutant, or EGFR-amplified, TERT promoter-mutant IDH-wildtype glioblastomas. The gene discussed is IDH1; the disease is oligodendroglioma.