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