For example, what was thought to be a uniform group of glioblastomas occurring in the posterior fossa, now comprises distinct molecular entities (based on methylation profiles), namely anaplastic astrocytoma with piloid features; glioblastoma, IDH wildtype; diffuse midline glioma H3 K27M mutant; and astrocytoma, IDH mutant (20). This evidence concerns the gene IDH1 and diffuse midline glioma.