On the basis of these findings, the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy (cIMPACT-NOW) update 5 suggests that IDH-mutant GBM should be denoted astrocytoma, IDH-mutant, grade 4, but notes that this change in this terminology may be viewed as controversial and will require further discussion in context of the next WHO classification11. The gene discussed is IDH1; the disease is astrocytoma (excluding glioblastoma).