Astrocytoma

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  • i. Astrocytic neoplasms are listed in the World Health Organization (WHO) classification as: astrocytoma (fibrillary, protoplasmic, and gemistocytic), anaplastic astrocytoma, glioblastoma, pilocytic astrocytoma, pleomorphic xanthoastrocytoma (PXA) and subependymal giant cell astrocytoma (SEGA)
    • 1. astrocytoma (mean survival 80 months), anaplastic astrocytoma (mean survival 21 months), and glioblastoma (mean survival 11 months) form an interrelated group
    • 2. glioblastomas account for 50% of intracranial gliomas
  • ii. genetic abnormalities
    • 1. astrocytomas have p53 gene mutation/17p chromosome loss (25-35%) or chromosome 22q loss
      • a. p53 (located on chromosome 17p) is the guardian of the genome and is a transciption factor that is usually low in replication but with DNA damage, p53 is phosphorylated (by the ataxia telangiectasia gene) product and its destruction is slowed
      • b. p53 also initiates apoptosis if DNA damage is too great for repair
    • 2. anaplastic astrocytomas have Rb gene mutations/chromosome 13q loss or 16p gene deletions/chromosome 9p loss or chromosome 19q loss
    • 3. glioblastomas have chromosome 10 loss or EGFR gene amplification however primary glioblastomas and astrocytomas that evolve into glioblastomas may have different genetic characteristics; usually have necrotic center which shows up as ring enhancing on CT scan
    • 4. tumor growth factor (TGF) beta-2 produced by gliomas downregulates interleukin-2 receptors of T lymphocytes
    • 5. T cell function is frequently impaired in glioma patients
    • 6. glioma resection improves T lymphocyte function
  • iii. prognostic indicators in astrocytic neoplasms
    • 1. age, Karnofsky performance score, histologic diagnosis, microcysts in astrocytoma, Ki-67 labeling index
  • iv. St. Anne/Mayo grading system factors (1 point for each)
    • 1. nuclear atypia
    • 2. mitoses
    • 3. capillary endothelial proliferation
    • 4. necrosis
    • 5. (Remember - gliomas are MEAN: mitoses, endothelial proliferation, atypia (nuclear), necrosis); St. Anne/Mayo grade = WHO grade except for grade I which is a pilocytic astrocytoma
  • v. pilocytic astrocytomas
    • 1. typically have biphasic appearance with some parts of the neoplasm with elongated cells arranged in compact fascicles while other places have stellate, fine branching processes
    • 2. pilocytic astrocytomas do not share the genetic abnormalities of other glial tumors, they do not infiltrate surrounding tissue in the same manner and rarely progress to an anaplastic form
    • 3. Rosenthal fibers (inclusions in astrocytes not found in other fibrillary astrocytomas) and intracellular eosinophilic globules are classic features and may be abundant; also see compact arrangement of elongated cells with some spindle shaped cells
    • 4. most label with antibodies to GFAP
    • 5. common sites of predilection are cerebellum, optic nerve, optic chiasm, hypothalamus, third ventricle, and temporal lobe
  • vi. pleomorphic xanthoastrocytoma (PXA)
    • 1. generally situated superficially in the cerebrum of children and young adults; generally have a more favorable course than other astrocytomas
    • 2. usually presents with epilepsy and commonly arises in the temporal lobe; often associated with a cyst
    • 3. cytoplasmic lipid droplets are found with some frequency
  • vii. subependymal giant cell astrocytoma (SEGA) (a.k.a. giant cell astrocytoma)
    • 1. tuberous sclerosis (TS) patients have SEGA 5% of the time
    • 2. TS inherited autosomal dominant (chromosome 9q or 16p)
    • 3. SEGA usually occurs around the lateral ventricle often with calcification; exophytic appr
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