IDH1 and glioma: The 2016 World Health Organization (WHO) classification of central nervous system (CNS) tumors that integrated isocitrate dehydrogenase (IDH) mutational status with histology in classifying gliomas, and the introduction of mutant IDH inhibitors (from here on: IDH inhibitors) into clinical practice has led to a reassessment of the biology and optimal therapies for grades 2 and 3 IDH-mutant gliomas.