world cancer report - iarc

TUMOURS OF THE NERVOUS SYSTEM
SUMMARY
> Tumours of the nervous system account
for less than 2% of all malignancies
(about 175,000 cases per year worldwide);
the incidence does not vary
markedly between regions or populations.
> Etiology is largely unknown; the only
unequivocal cause is therapeutic irradiation,
but occurrence in these circumstances
is very rare.
>The nervous system is frequently
involved in inherited tumour syndromes,
including neurofibromatosis (NF1/NF2
germline mutations), von Hippel-Lindau
disease (VHL), tuberous sclerosis
(TSC1/TSC2) and Li-Fraumeni syndrome
(p53).
> Glioblastomas are the most common
brain tumours and mainly affect adults.
These tumours are surgically incurable
and largely resistant to radiation and
chemotherapy; only 3% of patients survive
more than 3 years.
>Embryonal tumours, including cerebellar
medulloblastomas, retinoblastomas and
peripheral neuroblastoma, predominantly
afflict children, ranking second after
leukaemia as the most common types of
paediatric cancer.
Definition
The majority of tumours of the central
nervous system (CNS) are derived from
glial cells (gliomas), the most malignant
and frequent being glioblastoma. Malignant
embryonal tumours typically manifest
in children and occur in the central
nervous system (medulloblastomas) and
the sympathetic nervous system and adrenal
gland (neuroblastomas). Tumours originating
from the brain coverings (meningiomas)
are usually benign.
Epidemiology
The age distribution of brain tumours is
bimodal, with a peak incidence in children
and a second larger peak in adults aged
45-70 [1]. In most developed countries,
brain tumours are the 12 th most frequent
cause of cancer-related mortality in men
[2]. Geographical variation in incidence is
less than for most other human neoplasms
[2] (Fig. 5.149). However, incidence
tends to be higher in more developed
countries. In most North American
and European countries, incidence rates
for malignant tumours of the nervous system
are 6-8 new cases per 100,000 population
per year. Highest rates are
observed in Sweden, Greece, Iceland and
Croatia. In multiracial communities, both
adults and children of African or Asian
descent tend to be less frequently affected
than whites. It has been reported that
white Americans have a 3.5 times greater
risk of glioblastoma and germ cell
tumours than African Americans [1].
However, the lower incidence recorded
for Singapore and Japan may be due to
inadequate registration.
< 6.6 < 7.8 < 9.1 < 10.2 < 11.6
Age-standardized incidence/100,000 population
Fig 5.149 Incidence of cancers of the brain and nervous system in men, in Europe.
Generally, incidence rates are higher for
men; in particular, malignant brain tumours
occur more frequently in males while the
benign meningiomas occur predominantly
in females. During the past decade, the
incidence of glioblastomas in the elderly
has increased by 1-2% per year but to some
extent this may be due to the introduction
of high-resolution neuroimaging. The brain
is also a frequent site of metastases, with
carcinomas of the breast and lung as most
frequent primary tumours.
Etiology
With the exception of brain tumours associated
with inherited cancer syndromes and
the very rare cases caused by therapeutic
irradiation, no causative environmental or
lifestyle factors have been unequivocally
identified. Radiation-induced meningiomas
may follow low-dose irradiation for tinea
capitis (a fungal infection of the scalp) and
high-dose irradiation for primary brain
tumours [3]. Children who received prophylactic
CNS irradiation for acute lymphoblastic
leukaemia seem to have an increased risk
of developing malignant gliomas.
Tumours of the nervous system
265