Leading Work-Related Diseases and Injuries -- United States
The National Institute for Occupational Safety and Health
(NIOSH)
has developed a suggested list of the 10 leading work-related
diseases
and injuries (1). The first two categories, "Occupational Lung
Diseases" and "Musculoskeletal Injuries," were recently described
(1,2); a discussion of the third category, "Occupational Cancers
(Other than Lung)," appears below.
OCCUPATIONAL CANCERS (OTHER THAN LUNG)
Cancer kills approximately 430,000 people in the United States
annually; the American Cancer Society estimates that some form of
cancer will develop in one-fourth of all Americans (3). It is the
second leading cause of death and the second leading cause of lost
years of potential life in this country (4). A high proportion of
all
cancers are thought to be caused by "extragenetic" factors,
including
behaviors (e.g., cigarette smoking, alcohol and drug use, and
sexual
activities) and toxic environmental exposures in the workplace and
the
community (5). Evidence for these relationships has been developed
principally through epidemiologic and toxicologic studies. The
main
epidemiologic observations have included: differences in the
incidence of cancer between groups with different exposures,
changes
in the incidence of cancer following migrations, changes in the
incidence of cancer over time, etc. Toxicologic studies have led
to
the identification of specific agents that cause cancer in
experimental animals (5).
A possible occupational origin for malignant disease was first
recognized when an unusually high frequency of scrotal cancer was
observed among London chimney sweeps in 1775 (6). Since then,
several
types of cancer have been associated with industrial agents or
processes (Table 1) (7). Numerous other occupational agents--such
as
beryllium, cadmium, ethylene oxide, phenoxy-acetic acids, and
chlorophenols--or processes--such as newsprint pressroom work--are
suspected of being carcinogenic and are under investigation by
NIOSH.
Although general agreement exists concerning the overall
incidence
of cancer, considerable controversy surrounds the proportion of
cancer
cases attributable to occupational exposures. Several
characteristics
of cancer contribute to the difficulty in making such estimates:
Latency in the development of cancer. Occupational cancer
usually becomes evident long after initial exposure to the
carcinogen; this interval may vary from 5 years to more
than
40 years (9), making it difficult to characterize
important
exposures long past.
Influence of exposures to multiple carcinogens. Cancer
victims may have been occupationally exposed to many
carcinogens; interaction of these agents or interactions
between them and other factors may greatly increase the
risk
of cancer (10).
Influence of behavioral factors. Cigarette smoking,
alcohol
drinking, and dietary habits also influence the
development
of cancer (11). Moreover, these factors--especially
cigarette smoking--interact with chemical and physical
agents
in the working environment to increase the risk of cancer
(12); e.g., exposure to asbestos interacts with cigarette
smoking to greatly increase the risk of lung cancer.
In addition, problems with the documentation of cancer and the
nature and extent of etiologic exposures obscure important
epidemiologic associations:
Errors in diagnosis and classification of cancer. Unusual
neoplasms are often misdiagnosed; even correct diagnoses
may
be improperly categorized according to the International
Classification of Diseases (ICD); an example is
mesothelioma
(10).
Lack of meaningful occupational histories. In only a few
states is information collected on the work histories of
cancer victims; hence, for many cases, crucial
associations
with occupational carcinogens are not apparent.
Difficulty in assessing exposures quantitatively. Precise
measurements of levels and duration of exposures have not
generally been available (13). Consequently, the ability
to
delineate dose-response relationships has been very
limited.
The frequency of specific types of cancers. The
occupational
etiology of a very rare cancer due to a specific agent
(e.g.,
hemangiosarcoma of the liver due to vinyl chloride) is
much
more readily documented than the occupational etiology of
a
cancer type potentially caused by several factors (e.g.,
lung
cancer associated with exposure to chromates).
The "dilution factor." Highly significant differences in
the
rates of cancer among small subgroups of a population may
be
overlooked because these rates affect the overall rate for
cancer in the larger study population only slightly, if at
all (8).
Despite these difficulties, various attempts have been made to
estimate the proportion of cancers related to occupation. These
estimates span a broad range, from less than 4% (5,14) to more than
20% (15). While these estimates are obviously imprecise, little
doubt
remains that occupational factors are significantly related to an
increased risk of cancer. Moreover, in specific groups of workers
exposed to specific carcinogens, the proportion who ultimately
develop
occupational cancer may be large. Of one group of workers
distilling
beta-naphthylamine who had more than 5 years of exposure, all
reportedly developed tumors of the bladder (17); up to 11% of
workers
exposed to asbestos may ultimately develop mesothelial tumors (16).
Reported by Div of Surveillance, Hazard Evaluations, and Field
Studies, NIOSH, CDC.
Editorial Note
Editorial Note: Cancer caused by occupational agents, especially
synthetic chemicals, is a problem of human origin, and should,
therefore, be preventable. Substitution of noncarcinogens for
carcinogens, enforcement of protective standards for exposure,
design
and application of engineering controls, and use of personal
protective equipment by exposed workers are major modes of
prevention.
Although it is difficult to predict a trend for the future
incidence of occupational cancer, the increased volume and
diversity
of synthetic chemicals manufactured since World War II (18) raise
serious concern about the risks from exposure to these substances.
However, improved control technology, governmental regulatory
activity
to reduce exposures, surveillance of disease and risk factors, and
vigilant use of preventive measures will ultimately reduce
occupational cancer.
References*
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Doll R, Peto R. The causes of cancer: quantitative estimates
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_______________
Additional references are available on request from the National
Institute for Occupational Safety and Health, CDC.
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