IDH1 and astrocytoma (excluding glioblastoma): Amongst glioma subtypes, IDH1/2-mutant astrocytoma has experienced one of the largest shifts in the transition from histopathologic to molecular classification, with almost half of these tumors previously classified as glioblastoma or other non-astrocytic gliomas.3,7 As a result, IDH1/2-mutant astrocytoma reflects a clinically heterogenous group, with a broad range of survival outcomes, especially amongst grade 2 and grade 3 tumors.