world cancer report - iarc
world cancer report - iarc
world cancer report - iarc
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TOBACCO<br />
SUMMARY<br />
>In addition to lung <strong>cancer</strong>, tobacco<br />
consumption causes tumours of the larynx,<br />
pancreas, kidney, bladder and, in<br />
conjunction with alcohol drinking, a high<br />
incidence of carcinomas of the oral cavity<br />
and the oesophagus. In most developed<br />
countries, tobacco accounts for as<br />
much as 30% of all malignant tumours.<br />
> Lung <strong>cancer</strong> risk is determined by the<br />
amount of daily consumption of tobacco,<br />
duration of smoking and the depth of<br />
inhalation. For regular smokers, the relative<br />
risk for the development of lung <strong>cancer</strong><br />
is more than 20 times higher than for<br />
non-smokers. Environmental tobacco<br />
smoke (passive smoking) is also carcinogenic<br />
but the risk is much smaller (relative<br />
risk 1.15-1.2).<br />
> Tobacco smoke contains a great number<br />
of chemical carcinogens. The pattern of<br />
mutations in the p53 tumour suppressor<br />
gene in smoking-associated lung<br />
tumours suggests that benzo(a)pyrene<br />
metabolites play a major role in the<br />
development of lung <strong>cancer</strong>.<br />
> Cessation of smoking significantly<br />
reduces the risk of lung and other tobacco-associated<br />
<strong>cancer</strong>s, even after many<br />
years of addiction. However, even ten or<br />
more years after stopping smoking, the<br />
risk is somewhat greater than that of<br />
never-smokers.<br />
> Tobacco smoking is also the cause of<br />
various non-neoplastic ailments, including<br />
cardiovascular and obstructive lung<br />
diseases. The life expectancy of regular<br />
smokers is six to eight years less than<br />
that of people who have never smoked.<br />
Use of tobacco has been identified by<br />
WHO as the major preventable cause of<br />
death of humankind. The topic is<br />
addressed here only in relation to <strong>cancer</strong>,<br />
22 The causes of <strong>cancer</strong><br />
although tobacco smoking causes a range<br />
of cardiovascular and respiratory diseases<br />
[1]. Tobacco smoking causes <strong>cancer</strong> of<br />
the lung and other organs and is the most<br />
intensively investigated environmental<br />
cause of <strong>cancer</strong>. Most information available<br />
involves the burden of smoking-related<br />
disease in more developed countries;<br />
far less is known in relation to less developed<br />
countries, though predictions can be<br />
made with confidence.<br />
Preparation and use of tobacco<br />
The main tobacco plant in the <strong>world</strong> is<br />
Nicotiana tabacum, although some varieties<br />
of N. rustica are also cultivated and<br />
used. Tobacco was imported from North<br />
America to Europe, Asia and Africa in the<br />
second half of the 16th century. By the<br />
mid-17th century, tobacco was being<br />
grown for commercial purposes not only<br />
in the American colonies, but also in<br />
Europe and East Asia. Industrial production<br />
of cigarettes started in the second<br />
half of the 19th century.<br />
Tobacco needs to be cured before consumption.<br />
Two main curing processes are<br />
used. In flue-curing, the ripe leaves are cut<br />
and dried by artificial heat. Common<br />
names of flue-cured tobacco include<br />
“blond” and “Virginia”. In air-curing, the<br />
entire plant is harvested and no artificial<br />
heat is used. Air-cured tobacco includes<br />
“Maryland” and “black”. Cigars are also<br />
made of air-cured tobacco. Less important<br />
methods include sun-curing, fire-curing<br />
and various local adaptations. For “oriental”<br />
tobacco, sun- and air-curing are<br />
combined.<br />
Cigarettes represent the most important<br />
tobacco product <strong>world</strong>wide [2]. They are<br />
made from fine-cut tobacco wrapped in<br />
paper or maize leaf. The weight is between<br />
0.5 and 1.2 g. Tobacco may be sprayed<br />
with sugar and other flavouring or aromatic<br />
agents. Other smoking tobacco products<br />
include cigars and cigarillos (which<br />
vary greatly in size, weight and flavour and<br />
have many local names, e.g. cheroots,<br />
chuttas, stumpen), tobacco for pipes and<br />
water pipes, bidis (flaked tobacco rolled in<br />
a piece of dried temburni leaf), as well as<br />
many other local products. Tobacco is also<br />
chewed, alone or with lime, betel nut or<br />
other compounds [3]. The habit is prevalent<br />
in the Indian region and South<br />
America, but also in North America and<br />
Northern Europe.<br />
Tobacco snuff is taken in many countries,<br />
notably in Scandinavia, India and neighbouring<br />
countries, the Mediterranean and<br />
Southern Africa. The composition of chewing<br />
tobacco and snuff greatly varies geographically.<br />
In addition, other smokeless<br />
products are used in various parts of the<br />
<strong>world</strong> (e.g. “nass”, a mixture of tobacco,<br />
lime, ash, and other ingredients, in<br />
Central Asia).<br />
World production of tobacco is approximately<br />
seven million tonnes annually,<br />
China accounting for almost a third of this<br />
total [4]. Global trade in tobacco represents<br />
a major economic enterprise;<br />
although the USA and Europe lead the<br />
field, India and various nations of Africa<br />
are also major exporters (Table 2.1).<br />
Exposure<br />
The people most immediately exposed to<br />
the products of tobacco combustion are the<br />
Fig. 2.1 Tobacco market in Zimbabwe. In the<br />
developing <strong>world</strong>, tobacco consumption is<br />
increasing rapidly.