Anaplastic pilocytic astrocytoma

Anaplastic pilocytic astrocytoma, abbreviated APA, is an outdated tumor terminology. Most of these tumors are now classified either as High-grade astrocytoma with piloid features, Pleomorphic xanthoastrocytoma or as Glioblastoma, IDH-wildtype.

General

• High-grade astrocytoma - behaviour corresponded in older classifications to WHO Grade III.
• Some authors prefered the designation pilocytic astrocytoma with anaplastic features.
• Less than 2% of all pilocytic astrocytomas.
• De novo cases in the setting of neurofibromatosis 1 reported.
• Many tumors have history of previous radiation.

Old microscopic criteria

Features:

• At least 4 mitoses/10 high power fields - see HPFitis.
• Hypercellularity.
• Necrosis +/-.
• Pilocytic like (biphasic) - most common.
  1. Eosinophilic granular bodies +/-.
• Small cell (32%)
• Epithelioid cells (15%)
• Fibrillary areas resembling diffuse astrocytoma.

IHC

Features:

• GFAP +ve (fibres).
• p53: +ve.
• KI-67: high 25%.
• ATRX loss may be present.
• IDH1 (R132H) -ve.
• H3F3A (K27M) -ve.

See also

• Neuropathology tumours.
• Pilocytic Astrocytoma.