IDH1 and astrocytoma (excluding glioblastoma): Of note, both microdissected tumor pairs with detected inter- and intratumoral heterogeneities harbored the most frequent R132H IDH1- mutation in both their respective oligodendroglial and astrocytic tumor component, suggesting IDH1- mutation to be a common tumor initiating event in oligodendrogliomas, astrocytomas and oligoastrocytomas.