IDH1 and glioblastoma: According to the revised fourth edition of the WHO classification of brain tumors from 2016, malignant astrocytomas are furthermore differentiated based on their IDH status into the group of anaplastic astrocytomas WHO grade III with/without IDH mutation (AA IDH-mut/AA IDH-wt) and into the group of glioblastomas WHO grade IV with/without IDH mutation (GBM IDH-mut/GBM IDH-wt) [6].