IDH1 and astrocytoma (excluding glioblastoma): In the current (5th) edition of the World Health Organization (WHO) Classification of Tumors of the Central Nervous System (CNS), molecular alterations play a critical role in the diagnosis and grading of adult diffuse gliomas.1 For astrocytoma with isocitrate dehydrogenase (IDH) mutations (IDH1 or IDH2), investigators have attempted to risk-stratify survival based on patients’ molecular alterations.2 For the stratification of patients with IDH-mutant astrocytomas, the prognostic value of CNS WHO grade, which is primarily based on histologic parameters, remains controversial.