H3K27me3 is used as a diagnostic marker for diffuse midline glioma and as a surrogate marker to distinguish posterior fossa ependymoma A and B. However, the clinical significance of the EZH2–H3K27me3 axis in astrocytoma, IDH-mutant has not been reported, prompting this investigation. The gene discussed is EZH2; the disease is diffuse midline glioma.