GBM is a glioma and the most common type
of primary brain tumor. Gliomas are classified by the World Health Organization
into 4 distinct grades based on histological features of cellularity, nuclear
morphology, mitotic activity, necrosis, and vascular proliferation (Louis=et
alK, 2007).
A higher histologic grade corresponds to a
less differentiated phenotype and to increasing malignancy. The most common
form, a grade IV glioma, is called glioblastoma multiforme (GBM).
Accounts for more than one half of all gliomas and 15% to 20% of intracranial
tumors, GBM is the most common malignant primary brain tumor. It may occur at
any age but most commonly affects adults, with a peak incidence between 45 and
70 years of age. GBMs usually occur within the subcortical white matter, where
they may present de novo as a primary GBM or after dedifferentiation from
lower-grade glioma (secondary). It is thought that 60% of these tumors are de
novo in adults older than the age of 50 years. Secondary GBM typically develops
in younger patients under the age of 45 years through malignant progression from
a low-grade astrocytoma or AA.
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