cIMPACT-NOW update 5: recommended grading criteria and terminologies for IDH-mutant astrocytomas

Excerpt

The diagnostic importance of IDH mutational status in diffuse gliomas was first formally recognized within the updated 4th edition of the WHO Classification of Tumours of the Central Nervous System (2016). Its introduction as a diagnostic marker was based on evidence that incorporation of biomarkers into an integrated diagnosis provided a more reproducible and clinically meaningful classification of diffuse gliomas in adults [20‐22]. For IDH-mutant diffuse astrocytic gliomas, the integrated diagnostic entities (and corresponding grades) of the 2016 WHO Classification included diffuse astrocytoma, IDH-mutant (WHO grade II), anaplastic astrocytoma, IDH-mutant (WHO grade III) and glioblastoma, IDH-mutant (WHO grade IV). In contrast to IDH-mutant tumors, IDH-wildtype diffuse astrocytic gliomas are now recognized as distinct clinical and genetic entities that usually have much more aggressive clinical behavior, particularly in adults [5, 13]. While these molecular classifications represented a major step forward, grading schemes for the new diagnostic classes were not modified in parallel. The current grading criteria for diffuse astrocytic gliomas were developed prior to the understanding of molecularly distinct entities, yet the 2016 WHO update applies these same grading criteria for both IDH-mutant and IDH-wildtype astrocytic gliomas [11, 14]. …