D2HGDH and oligoastrocytoma: In the TCGA study, there were significant differences in HBEGF and D2HGDH expression between GB and non-GB subtypes (astrocytoma (P = 3.50 × 10−8 and 4.50 × 10−12, respectively), oligoastrocytoma (P = 1.00 × 10−8 and 4.90 × 10−12, respectively) and oligodendroglioma (P = 1.90 × 10−10 and P = 1.40 × 10−20)).