world cancer report - iarc
world cancer report - iarc
world cancer report - iarc
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poorly known since hypopharyngeal <strong>cancer</strong><br />
deaths are often mis-certified as deaths from<br />
<strong>cancer</strong> of the larynx.<br />
Carcinomas of the salivary glands and<br />
nasopharynx are distinguished from head<br />
and neck <strong>cancer</strong>s at other sites both by epidemiology<br />
and by etiology. Nasopharyngeal<br />
<strong>cancer</strong> is relatively rare on a <strong>world</strong> scale<br />
(65,000 new cases per year, or 0.6% of all<br />
<strong>cancer</strong>s), but it has a very distinctive geographic<br />
distribution. Age-standardized incidence<br />
rates are high for populations living in<br />
or originating from Southern China, whilst<br />
populations elsewhere in China, South East<br />
Asia, North Africa, and the Inuits (Eskimos) of<br />
Canada and Alaska, all have moderately elevated<br />
rates (Fig. 5.90). Males are more often<br />
affected than females (sex ratio 2–3:1), and<br />
in most populations, there is a progressive<br />
increase in risk with age. In moderate-risk<br />
populations, however, most notably in North<br />
Africa, there is a peak in incidence in adolescence.<br />
There appears to have been a<br />
decrease in incidence over time in some<br />
high-risk populations (e.g. Hong Kong).<br />
Etiology<br />
Smoking and drinking are the major risk factors<br />
for head and neck <strong>cancer</strong> in developed<br />
countries, in the Caribbean and in South<br />
American countries [1-3]. Smoking is estimated<br />
to be responsible for about 41% of<br />
laryngeal and oral/pharyngeal <strong>cancer</strong>s in<br />
men, and 15% in women <strong>world</strong>wide and<br />
these proportions vary amongst different<br />
populations. Tobacco smoking has also been<br />
found to be an important risk factor for<br />
nasopharyngeal <strong>cancer</strong> in otherwise low-risk<br />
populations. These risk factors have been<br />
shown, for laryngeal and oropharyngeal <strong>cancer</strong>s,<br />
to have a joint “multiplicative” or synergistic<br />
effect.<br />
In the Indian subcontinent, chewing tobacco<br />
in the form of betel quid (a combination of<br />
betel leaf, slaked lime, areca-nut and tobacco<br />
with or without other condiments), bidi (a<br />
locally hand-rolled cigarette of dried temburni<br />
leaf containing coarse tobacco) smoking<br />
and drinking locally brewed crude alcoholic<br />
drinks are the major causative factors.<br />
The role of betel quids without tobacco is not<br />
clear, though a recent case-control study<br />
from Pakistan <strong>report</strong>ed a high risk of oral<br />
<strong>cancer</strong> [4]. Reverse smoking (in which the lit<br />
Fig. 5.89 The global incidence of <strong>cancer</strong> of the larynx in men. High-risk countries are found in Southern<br />
and Eastern Europe, Latin America and Western Asia.<br />
end of the cigarette is placed in the mouth so<br />
that an intense heat is experienced) is a risk<br />
factor for <strong>cancer</strong> of the hard palate. Oral<br />
snuff use is an emerging risk factor for oral<br />
<strong>cancer</strong>, particularly among young males in<br />
the USA.<br />
A generally impoverished diet, particularly<br />
lacking in vegetables and fruits, is another<br />
risk factor for oral <strong>cancer</strong> [5]. Consistently,<br />
studies also indicate a protective effect of a<br />
diet rich in vegetables and fruits (20-60%<br />
reduction in risk). A high intake of salted fish<br />
and meat and the release of nitrosamines on<br />
cooking such foods have been linked to<br />
nasopharyngeal <strong>cancer</strong> in endemic regions.<br />
Oral human papillomavirus (HPV) infection<br />
(transmitted sexually or perinatally) is associated<br />
with an increased risk of head and neck<br />
squamous cell carcinoma development [6].<br />
Overall estimates for HPV prevalence in head<br />
and neck squamous cell carcinoma are very<br />
variable, ranging from 8-100%, but an unusual<br />
laryngeal pathologic subtype, verrucous<br />
laryngeal carcinoma, has a 100% prevalence<br />
of HPV. Tumours of the oropharynx (and in<br />
particular, tonsillar tissue) have been found<br />
to be three times more likely to be HPV-positive<br />
than tumours at other head and neck<br />
sites. Women with a history of in situ or inva-<br />
< 2.4 < 3.7 < 5.8 < 8.5<br />
Age-standardized incidence/100,000 population<br />
< 20.1<br />
sive cervical carcinoma have a two to fourfold<br />
increased risk of oral or laryngeal <strong>cancer</strong>,<br />
in addition to increased risks of other <strong>cancer</strong>s<br />
associated with HPV. Additional risk factors<br />
implicated in <strong>cancer</strong> of the larynx include<br />
chronic laryngitis, chronic gastric reflux and<br />
exposure to wood dust, asbestos or ionizing<br />
radiation.<br />
Infection with Epstein-Barr virus is important<br />
in the etiology of nasopharyngeal <strong>cancer</strong>.<br />
This virus is not found in normal epithelial<br />
cells of the nasopharynx, but is present in all<br />
nasopharyngeal tumour cells, and even in<br />
dysplastic precursor lesions [7] (Chronic<br />
infections, p56).<br />
Detection<br />
Although many head and neck <strong>cancer</strong>s arise<br />
in anatomically accessible areas, delayed<br />
diagnosis is common. Symptoms of oral <strong>cancer</strong><br />
include pain, bleeding, difficulty in opening<br />
the mouth, chewing, swallowing and<br />
speech, and a swelling in the neck. Early<br />
lesions are often painless and present as<br />
slightly elevated, velvety red mucosal patches,<br />
as punctate lesions, or as indurated small<br />
ulcers or growths. In more advanced stages,<br />
a large ulceroproliferative mass, with areas of<br />
necrosis, and extension to neighbouring<br />
Head and neck <strong>cancer</strong><br />
233