Precise classification of nervous system tumors into coherent clinicopathologic entities is the necessary first step for the appropriate management of patients. While this has been traditionally performed by histopathology only, recent accelerations in our understanding of the molecular features of nervous system tumors have led to the integration of molecular characteristics into diagnostic criteria. The updated WHO 2016 classification of tumors of the central nervous system (CNS)1 thus includes both histologic and molecular features—primarily mutational status of individual genes and copy number alterations—facilitating the precise diagnosis of CNS tumors. While this has led to increased objectivity and reproducibility, classification progress is still required, especially for rare and for poorly understood entities.