world cancer report - iarc

cating that exposure to asbestos caused
lung cancer accumulated from the 1930s
and the evidence became conclusive during
the 1950s and 1960s. However, only
during the late 1970s were effective steps
for limiting exposure initiated in some
countries [4]. Even so, relatively little
action concerning asbestos-induced cancer
has been taken in many countries
(notably in the developing world, see
below) until recently.
After introduction of preventive measures,
a progressive decrease in the risk of cancer
among relevant workers may be evident.
This may be seen by comparing
groups of workers who were employed in
different time periods. For example, the
risk of lung cancer decreased among
cohorts of American workers who were
potentially exposed to chloromethyl
ethers. This hazard was reduced after
1971, when a closed manufacturing system
was introduced [5]. Among relevant
workers, lung cancer incidence was greatest
in the 1960s, and decreased after
1974. Change in risk of cancer is also evident
amongst Norwegian workers
employed in a nickel refinery smelter from
the beginning of operation in the 1910s
until the 1960s [6] (Fig. 4.9). Major
changes in the process occurred during
this time, particularly after 1950. [7]. Risk
of nasal cancer has decreased; excess
risk of lung cancer has also decreased but
to a lesser degree, which may be attributable
to the effects of increased smoking.
The situation in developing countries
Most documented examples of successful
prevention of occupational cancer involve
developed countries. To some extent, these
examples have also led to improvement in
conditions of occupational hygiene in developing
countries. The quality of industrial
hygiene in the Chinese chemical industry
improved markedly during the 1970s such
that by 1981, air concentrations of vinyl
chloride monomer were similar to those in
industries in Europe and North America [8].
However, lack of economic resources and
health services may limit the adoption of
preventive measures. Often, exposure levels
in the informal employment sector and
in small workshops, where a large propor-
Fig. 4.9 Risk of lung cancer among nickel refinery workers, by year of first employment.
Fig. 4.10 UK asbestos imports and predicted mesothelioma deaths in British men. Mortality from
mesothelioma reflects past exposure to asbestos. Despite the ban on the use of asbestos in the early
1990s, mesothelioma cases will continue to increase, with approximately 250,000 expected deaths in
Europe over the next 35 years.
tion of workers are located in developing
countries, are high compared to “best practice”
adopted in large facilities [9].
Protective clothing may have limited effectiveness
in some developing countries
because of discomfort arising from its use
in hot, humid climates. Exposure to
asbestos, crystalline silica and pesticides
are recognized priorities for control of occupational
cancer hazards in developing countries.
The greatest impact in terms of pre-
vention of disease is likely to come from the
establishment and enforcement of national
and international regulatory controls.
Child labour is another cause for concern.
Even where regulations to protect workers
from exposures to carcinogens are adopted,
such regulations may not apply to children,
who are often not employed legally [8].
Some nations have established legislation
that applies specifically to the employment
of children: for example, a detailed list of
Reduction of occupational and environmental exposures 137