world cancer report - iarc

OCCUPATIONAL EXPOSURES
SUMMARY
> Many occupations and some specific
chemicals encountered at work are associated
with increased risk of cancer.
> Occupational cancer most often involves
the lung; other sites affected include the
skin, urinary tract, nasal cavity and pleura.
> Most occupational carcinogens have
been eliminated from the workplace.
However, in newly-industrialized countries,
relevant exposures still pose a significant
health risk.
> Some past exposures still carry a significant
cancer burden; in most European
countries, use of asbestos was banned
in the 1990s, but the peak mesothelioma
incidence will occur around 2020.
The first reports of associations between
risk of cancer and employment in particular
occupations appeared during the
18th century (scrotal cancer among
chimney sweeps [1]) and 19th century
(bladder cancer in workers exposed to
dyes [2]). However, the majority of studies
establishing a link between an
increased risk of cancer and a particular
working environment were published
between 1950 and 1975 [3]. Relatively
few occupational carcinogens have been
identified in the last 25 years.
Identifying hazardous materials
The IARC Monographs on the Evaluation
of Carcinogenic Risks to Humans evaluate
data relevant to the carcinogenic hazard
to humans as a consequence of
exposure to particular chemical, physical
and biological agents and mixtures [4].
Accordingly, evidence of carcinogenicity
for most known or suspected occupational
carcinogens has been evaluated in
the IARC Monographs programme. At
present, 25 chemicals, groups of chemi-
cals or mixtures for which exposures are
mostly occupational, have been established
as human carcinogens (Table 2.7).
While some of these agents, such as
asbestos, crystalline silica and heavy
metals, are currently encountered in the
workplaces of many countries, other
agents have been phased out and are
mainly of historical interest (e.g. mustard
gas and 2-naphthylamine).
An additional 25 agents presenting a
hazard on the basis of workplace exposure
are classified as probably carcinogenic
to humans. Most of these agents
have been shown to be carcinogenic in
experimental animals, and less than conclusive
evidence of carcinogenicity in
humans from epidemiological studies is
available. They include chemicals and
consequent exposures that are commonly
in many countries, such as those
associated with the use of formaldehyde
and 1,3-butadiene (Table 2.8). In many
instances, it is possible to associate
Fig. 2.16 The first cases of occupational cancer
identified were scrotal cancers in chimney
sweeps, in the late 18th century.
increased risk of cancer with a group of
agents or a particular work environment
rather than with a single compound. The
hazard posed by polycyclic aromatic
hydrocarbons is of particular interest.
Although several individual polycyclic
aromatic hydrocarbons are experimental
carcinogens (three of them are listed in
Table 2.8), human exposure always
involves complex mixtures of these
chemicals, often in variable proportions
(e.g. soots, coal tars). Therefore, the
determination of a hazard to humans
must involve consideration of such mixtures
and not the individual compounds.
A large number of agents primarily
encountered in an occupational context
are classified as possibly carcinogenic to
A
B
Fig. 2.17 Asbestos insulation is common in buildings
and presents a hazard when disturbed during
demolition. (A) Protective clothing must be worn
to avoid contact with (B) asbestos fibres .
Occupational exposures 33