world cancer report - iarc

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