Anaplastic astrocytoma (AKA: high-grade astrocytoma) is a infiltrating neoplasm of the diffuse astrocytic and oligodendroglial tumor group occurring in the CNS white matter.
- Most common grade III WHO glioma in adults (peaks between 40-50 years).
- Approx 5% of all gliomas.
- Usually shows progression to glioblastoma sooner or later.
WHO 2016 categorization combines morphology and genetics into following groups:
- Anaplastic astrocytoma, IDH-mutant (ICD-O: 9401/3).
- Anaplastic astrocytoma, IDH-wildtype (ICD-O: 9401/3).
- Anaplastic astrocytoma,NOS (ICD-O: 9401/3) - genetic data missing.
- Mass effect.
- Neurologic decifit.
- The majority are contrast-enhanching, T2 bright.
- Overall prognosis is rather poor (average survival 2-3 years).
- IDH-mutant tumors share a similiar prognosis to grade II IDH-mutant tumors.
- Anaplastic astrocytoma, IDH-wildtype perform worse than glioblastoma, IDH-mutant despite grading differences.
- No clear demarcation from white matter.
- Invaded structures may appear enlarged.
- Softer consistency and opacity.
- No necrosis.
- Increased cellularity (compared to Diffuse Astrocytoma).
- Specimens with low cellularity but plenty mitoses are also considered anaplastic.
- Distinct nuclear atypia and pleomorphism.
- May include multinucleated cells.
- Cytoplasm highly variable (even within the same tumour).
- Mitoses present (a single mitosis in a small specimen indicates a high-grade tumor).
- Microcystic spaces of the background (none to extensive).
- No necrosis, no vascular proliferations.
- Except radiation necrosis after pretreatment.
- Lymphocytic cuffing (mostly in gemistocytic type).
- Rosenthal fibers usu. absent.
- MAP2+ve (especially in cell processes).
- Vimentin+ve (often perinuclear).
- MIB-1: usu. 5-10& (overlaps with grade II tumors).
- IDH-1 (R132H)+ve in 60-70%.
- 'Note: This antibody does not detect other rare IDH1/2 mutations.
- ATRX nuclear loss in 70%.
- TERT promotor mutations in 20-25%
- Approximately 80 % of IDH wildtype astrocytomas in fact represent underdiagnosed GBM.
- Diffuse astrocytoma - absent or very low mitotic activity.
- Anaplastic Oligoastrocytoma, NOS - esp. when genetic data on IDH and LOH 1p/19q are lacking.
- Anaplastic Oligodendroglioma, when LOH 1p/19q is present.
- Glioblastoma - vascular proliferations and / or necrosis.