## Genetic Profile of Diffuse Astrocytoma (WHO Grade II) **Key Point:** Diffuse astrocytomas are characterized by IDH1/IDH2 mutations (present in ~80% of cases) combined with TP53 mutations, which define the isocitrate dehydrogenase (IDH)-mutant astrocytoma category. **High-Yield:** The IDH1 R132H mutation is the most common point mutation in low-grade gliomas and is associated with a better prognosis than IDH-wild-type tumors. ### Molecular Classification of Gliomas | Feature | Diffuse Astrocytoma (Grade II) | Anaplastic Astrocytoma (Grade III) | Glioblastoma (Grade IV) | | --- | --- | --- | --- | | IDH mutation | Present (~80%) | Present (~60%) | Rare (IDH-wt more common) | | TP53 mutation | Common (~50–70%) | Common (~70%) | Variable | | EGFR amplification | Rare | Rare | Common (primary GBM) | | Chr 10 loss | Rare | Rare | Common | | 1p/19q codeletion | Absent | Absent | Absent | **Clinical Pearl:** IDH-mutant astrocytomas have a significantly better prognosis than IDH-wild-type counterparts, with median overall survival extending to 10+ years for Grade II tumors. **Mnemonic:** **IDHA** = IDH mutation + TP53 = Astrocytoma (low-grade). Remember: astrocytomas are IDH-mutant; oligodendrogliomas have 1p/19q codeletion. [cite:Robbins 10e Ch 28] 
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