Oligoastrocytoma pathophysiology

Oligoastrocytomas are mixed tumors that arise from the proliferation of both oligodendrocytes and astrocytes. Genes associated with the pathogenesis of oligoastrocytoma and anaplastic oligoastrocytoma include IDH1, p53, EGFR, ATRX, EGFR, PTEN, MGMT, CIC, and FUBP1. 30-70% of oligoastrocytomas show loss of heterozygosity (LOH) of 1p and 19q. On gross pathology, oligoastrocytoma is characterized by a soft, well-defined, grey-tan, mucoid or hemorrhagic, calcified mass with or without necrosis, which may expand the gyrus and cause blurring of the grey-white junction. On microscopic histopathological analysis, oligoastrocytoma is characterized by highly cellular lesions composed of both oligodendroglial and astrocytic components. In addition to the histological features of oligoastrocytoma, anaplastic oligoastrocytoma also has significant or brisk mitotic activity, marked cytologic and nuclear atypia, necrosis, apoptosis, and microvacular proliferation. Oligoastrocytoma is demonstrated by positivity to tumor markers such as MAP2, GFAP, IDH1, OLIG-1 protein, OLIG-2 protein, and Iba-2 protein.

• Oligoastrocytomas are mixed tumors that arises from the proliferation of both oligodendrocytes and astrocytes.^[1]
• Oligoastrocytomas are low-grade (grade II) tumors and anaplastic oligoastrocytomas are high-grade (grade III) tumors that occur in the brain.^[2]

• Development of oligoastrocytoma is the result of multiple genetic mutations.
• Oligoastrocytomas are mixed tumors that have overlapping molecular genetics with both oligodendrogliomas and astrocytomas.^[3]
• 30-70% of oligoastrocytomas show loss of heterozygosity (LOH) of 1p and 19q.^[3][4][5]
• Genes associated with the pathogenesis of oligoastrocytoma and anaplastic oligoastrocytoma include:^{[3][6][7][8][9][10][11][4]}

• IDH1
• p53
• EGFR
• ATRX
• EGFR
• PTEN
• MGMT
• CIC
• FUBP1

• On gross pathology, oligoastrocytoma is characterized by a soft, well-defined, grey-tan, mucoid or hemorrhagic, calcified mass with or without necrosis, which may expand the gyrus and cause blurring of the grey-white matter junction.^[4]
• Oligoastrocytomas are commonly found in the supratentorial region.
• Common intracranial sites associated with oligoastrocytoma include:^{[12][13][14][3]}
  • Frontal lobe (most common)
  • Temporal lobe
  • Parietal lobe
  • Occipital lobe
  • Insula
  • Diencephalon
  • Spinal cord

On microscopic histopathological analysis, oligoastrocytoma is characterized by:^{[15][16][17][18][19]}

• Highly cellular lesions composed of both oligodendroglial and astrocytic components
• Two types of pattern: biphasic and diffuse
  • Biphasic pattern demonstrates oligodendroglial and astrocytic differentiation, whereas diffuse pattern demonstrates intermingling of both the components
• Oligodendrocytes
  • Fried-egg shaped cells
  • Composed of minigemistocytes
  • Round nucleus
  • Distinct cell borders
  • Moderate-to-marked nuclear atypia with speckled “salt-and-pepper” chromatin pattern and perinuclear halo
  • Focal microcalcification
• Astrocytes
  • Star-shaped cells
  • Composed of gemistocytes
  • Multinucleated giant cells
  • Ovoid nucleus
  • Nuclear atypia

On microscopic histopathological analysis, anaplastic oligoastrocytoma is characterized by:^[15][16][17]

• Significant or brisk mitotic activity (≥ 6 mitoses per 10 high power field)
• Marked cytologic and nuclear atypia
• Necrosis
• Apoptotic cells
• Microvacular proliferation
  • ‘Glomeruloid’ vessels or endothelial hyperplasia

• 
  _{Biopsy specimen of an oligoastrocytoma (HE stain).^[20]}

Oligoastrocytoma is demonstrated by positivity to tumor markers such as:^{[21][22][11][23][4]}

• MAP2
• GFAP
• IDH1
• OLIG-1 protein
• OLIG-2 protein
• Iba-2 protein
• ID4 protein
• Ki-67
• Vimentin
• Synaptophysin

• 
  _{Histology of oligoastrocytoma cells demonstrating positivity to tumor marker GFAP.^[24]}
• 
  _{Histology of oligoastrocytoma cells demonstrating positivity to tumor marker Ki-67.^[25]}

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