Since its introduction in the 1970s, the clinical diagnostics field rapidly advanced wherein pathologists can better classify tumors based on their expression of lineage-specific markers (glial tumors selectively expressing GFAP), oncogenic somatic mutations (oligodendrogliomas express IDH1 R132H mutation), and epigenetic modifications (diffuse midline gliomas show H3K27me3 loss) (26, 27). The gene discussed is IDH1; the disease is glioma.