The most accurate diagnostic classification incorporates assessment of any accompanying alterations, such as those commonly co-occurring with IDH1/2 mutation (e.g. TP53 and ATRX mutation in astrocytomas vs. CIC, FUBP1, and TERT promoter mutations in oligodendrogliomas) or with BRAF mutation/fusion (e.g. CDKN2A homozygous deletion in PXA versus intact CDKN2A alleles in ganglioglioma and pilocytic astrocytoma) [6, 29, 30, 34, 44]. The gene discussed is IDH1; the disease is oligodendroglioma.