world cancer report - iarc

ing the optic tract, brain stem and spinal
cord. It infiltrates adjacent brain structures
but grows slowly and usually has a
favourable prognosis with five-year survival
rates of more than 85% (WHO Grade
I). Some pilocytic astrocytomas occur in
the setting of neurofibromatosis type 1
(NF1), particularly those of the optic nerve
(optic glioma). Other astrocytomas usually
develop in the cerebral hemispheres of
adults and diffusely infiltrate adjacent
brain structures.
Low grade diffuse astrocytomas (WHO
grade II) occur in young adults and grow
slowly. However, they diffusely infiltrate
the brain and cannot, therefore, be completely
surgically resected.
Morphologically, tumour cells resemble
differentiated astrocytes. Mutations in
p53 are found in two-thirds of cases and
are considered an early event. The fiveyear
survival rate is more than 60%.
Anaplastic astrocytomas (WHO grade III)
often develop from low-grade astrocytomas,
grow relatively fast and typically
progress to glioblastoma within two to
three years, accompanied by genetic alterations,
including loss of heterozygosity
(LOH) on chromosome 19.
Glioblastomas (WHO grade IV)
This is the most frequent and most malignant
nervous system tumour. Secondary
glioblastomas develop by malignant progression
from low-grade and anaplastic
astrocytoma and are characterized by p53
mutations and LOH on chromosome 10q.
Primary glioblastomas are more frequent
(>80% of cases) and develop rapidly in the
elderly (mean age, 55 years), with a short
clinical history of less than three months.
Their genetic profile includes amplification
and overexpression of the EGF receptor
gene, PTEN mutations, p16 INK4A deletions
and loss of chromosome 10. Both glioblastoma
types diffusely infiltrate the brain,
including the opposite hemisphere and
show high cellularity and large areas of
necrosis despite excessive vascular proliferation.
Oligodendrogliomas
These neoplasms develop from myelinproducing
oligodendroglial cells or their
Fig. 5.151 An MRI scan of a primary glioblastoma in a 79 year-old patient. A small cortical lesion rapidly
developed into a full-blown glioblastoma with perifocal oedema and central necrosis.
precursors and are typically found in the
cerebral hemispheres of adults, often
including the basal ganglia. Histologically,
they are isomorphic, with a typical honeycomb
pattern and delicate tumour vessels
(“chicken wire” pattern). Anaplastic
oligodendrogliomas (WHO Grade III) show
features of anaplasia and high mitotic
activity and carry a less favourable prog-
nosis. Genetic hallmarks of oligodendrogliomas
are LOH on chromosomes 1p
and 19q. Oligodendrogliomas that carry
these genetic alterations show a remarkable
sensitivity to chemotherapy.
Ependymomas
These gliomas develop from the ependymal
lining of the cerebral ventricles and
Differentiated astrocytes or precursor cells
mutation (>65%)
α
overexpression ( ~ 60%)
Low grade astrocytoma
( ~ 50%)
alteration ( ~ 25%)
Anaplastic astrocytoma
mutation (5%)
loss of expression ( ~ 50%)
α amplification (