Anaplastic Astroblastoma
⚠️ Terminology Note (WHO CNS 2021)
Anaplastic astroblastoma is no longer a recognized standalone diagnosis in the 2021 WHO Classification of CNS Tumors.
Only the entity “Astroblastoma MN1-altered“ is currently valid, and it requires molecular confirmation of MN1 gene rearrangement.
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🧠 Historical Definition
Previously described as a rare glial tumor, often in children and young women, with the following features:
- Perivascular pseudorosettes (astroblastic rosettes)
- High cellularity
- Nuclear atypia
- Mitotic activity
- Palisading necrosis
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🔬 Diagnostic Criteria (Current WHO Standards)
Astroblastoma, MN1-altered
- Histology: Astroblastic pseudorosettes
- Molecular requirement: MN1 gene fusion (e.g., MN1::BEND2)
- Detection: FISH, RT-PCR, or RNA sequencing
If MN1 fusion is absent
- The tumor should not be called “astroblastoma”
- Reclassify as one of:
- High-grade glioma, NOS
- High-grade neuroepithelial tumor, NOS
- Or another defined entity (based on methylation profiling)
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🧪 Molecular Comparison Table
| Marker | MN1-altered Astroblastoma | Non-MN1 / Anaplastic-Like Tumors |
|---|---|---|
| MN1 fusion | ✅ Required | ❌ Not detected / Not tested |
| IDH1 mutation | ❌ Negative | ✅ Negative |
| ATRX expression | ✅ Retained | ✅ Retained |
| P53 expression | ❌ Usually negative | ✅ Positive |
| Ki-67 proliferation | ❌ Low to moderate | ✅ High (e.g., 20%) |
| CDKN2A / RB1 status | ❌ Typically intact | ✅ Deletion present |
| MGMT methylation | Variable | ❌ Unmethylated (→ TMZ resistance) |
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🧾 Suggested Diagnostic Label (if MN1 not confirmed)
High-grade neuroepithelial tumor, NOS, *with histological features compatible with anaplastic astroblastoma but lacking MN1 rearrangement.*
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🧪 Recommendation
Consider additional testing:
- Methylation profiling (e.g., Heidelberg Classifier)
- RNA sequencing to confirm or rule out MN1 fusion
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📌 Summary
- “Anaplastic astroblastoma” is now a descriptive, not diagnostic term
- Only tumors with confirmed MN1 alteration qualify for the diagnosis “Astroblastoma, MN1-altered”
- Molecular testing is mandatory for classification under WHO CNS 2021