In brief, after their initial discovery in glioblastomas arising from lower-grade precursor lesions, so called “secondary” glioblastomas in 2008 [4], it became rapidly evident that IDH-mutations are typical for diffuse lower grade astrocytomas and oligodendrogliomas [5, 6] and associate with a far better prognosis than diffuse IDH-wildtype gliomas [7] most frequently resembling glioblastomas, IDH-wildtype [8]. Here, IDH1 is linked to oligodendroglioma.