Based on well-documented associations between occupational exposures
and cancer, it is estimated that approximately 20,000 cancer deaths and
40,000 new cases of cancer each year in the U.S. are attributable to
Millions of U.S. workers are exposed to substances that have tested
as carcinogens in animal studies. However, less than 2% of chemicals in commerce have been tested for
Cancer is a group of different diseases that have the same feature,
the uncontrolled growth and spread of abnormal cells. Each different
type of cancer may have its own set of causes. Many factors play a role
in the development of cancer. The importance of these factors is
different for different types of cancer. A person's risk of developing
a particular cancer is influenced by a combination of factors that
interact in ways that are not fully understood. Some of the factors
- Personal characteristics such as age, sex, and race
- Family history of cancer
- Diet and personal habits such as cigarette smoking and alcohol
- The presence of certain medical conditions
- Exposure to cancer-causing agents in the environment
- Exposure to cancer-causing agents in the workplace
In many cases, these factors may act together or in sequence to
Worker pulling a hydraulic cleaner from an open vinyl chloride
reactor at Avon Lake, OH in 1974, prior to the exposure controls
mandated by the OSHA standard. Vinyl chloride is known to cause
angiosarcoma of the liver.
Three members of the staff of an elementary school were diagnosed
with cancer in 1997 and 1998; one person each with brain, liver, and
ovarian cancer. Since 1998, four cases of breast cancer also were
diagnosed. Increased concern among employees regarding the potential
association between the workplace and the cancers prompted a request
for an investigation.
The information below addresses cancer clusters in general and shows
how this type of information would be used to respond to this
Cancers often appear to occur in clusters, which scientists define
as an unusual concentration of cancer cases in a defined area or time.
A cluster also occurs when the cancers are found among workers of a
different age or sex group than is usual. The cases of cancer may have
a common cause or may be the coincidental occurrence of unrelated
causes. Although the occurrence of a disease may be random, the
distribution of that disease may not be uniform, and clusters of
disease may arise by chance alone. When cancer in a workplace is
described, it is important to determine the primary site of the
What do we look for when evaluating a cancer cluster?
Because cancer is a common disease, cancer can be found among
people at any workplace. In the United States, one in two men and
one in three women will develop cancer over the course of their
lifetime. These figures show the unfortunate reality that cancer
occurs more often than many people realize. Disease or tumor rates
are very variable in small populations and rarely match the overall
rate for a larger area, such as the state, so that for any given
time period some populations have rates above the overall rate and
others have rates below the overall rate. So, even when there is an
excess, this may be completely consistent with the expected random
Worker handling amosite asbestos, which is known to cause lung
cancer and mesothelioma, at a pipe insulation manufacturing plant
in Tyler, TX, in the early 1970s.
In the scenario above, 95 staff members had worked at the school
since it opened in 1992. Breast cancer is the most common type of
cancer in women, affecting an estimated one of every eight women.
Because the school's workforce was primarily composed of women, it
was not unusual to see several cases of breast cancer. Although
these breast cancers were diagnosed within a relatively short time
frame, this made sense given the age of the staff and the age
distribution for breast cancer.
Cancer clusters thought to be related to a workplace exposure
usually consist of the same types of cancer. When several cases of
the same type of cancer occur and that type is not common in the
general population, it is more likely that an occupational exposure
is involved. When the cluster consists of multiple types of cancer,
without one type predominating, an occupational cause of the
cluster is less likely.
In our example, four types of cancer were diagnosed among the
elementary school staff.
When a known or suspected cancer-causing agent is present and
the types of cancer occurring have been linked with these exposures
in other settings, we are more likely to make the connection
between cancer and a workplace exposure. We also look to see
whether cancer is occurring among employees in particular jobs or
areas of the workplace. This can help to identify exposures.
School environments do not typically contain significant
hazardous exposures. Asbestos can be a concern in older buildings,
but while it is known to cause lung cancer and mesothelioma, it is
not known to cause the types of cancer reported among this group of
The time between first exposure to a cancer-causing agent and
clinical recognition of the disease is called the latency period.
Latency periods vary by cancer type, but usually are 15 to 20
years, or longer. Because of this, past exposures are more relevant
than current exposures as potential causes of cancers occurring in
workers today. Often, these exposures are hard to document.
The average time from first employment in the school to the
diagnosis of cancer among staff members in the elementary school in
our example was 5.7 years.
Conclusions for the scenario above
Workers on top of a coke oven. Work on top of coke ovens is known to
cause lung and skin cancer, and thought to cause kidney cancer.
The distribution of types of cancer did not appear unusual given the
age and gender of the employees. No known biologically significant
exposures were identified. The building only became occupied in 1992,
therefore, given what we know about latency periods, none of the cancer
cases met the latency criterion. Given this information, it was
concluded that the cancers reported among these workers were unlikely
to be the result of employment at the elementary school.
This scenario illustrates the key questions that are answered in
response to cancer cluster inquiries. Historical experience at NIOSH
has shown that most reports of cancer clusters indicate the
coincidental occurrence of cancer in workforce members. In most
situations, particularly in non-industrial work environments, it is not
possible to link the cancers to exposures at work.
National Academies Evaluation
Worker and Public Health Activities Program Administered by the Department
of Energy and the Department of Health and Human Services – Evidence Package
General: Causes, Specific Diseases
Regulation and Policy
External link: http://www.osha.gov/SLTC/carcinogens/standards.html
- Occupational Respiratory Disease Surveillance (ORDS)
Occupational respiratory disease medical screening and monitoring
- Work-Related Lung Disease Surveillance Report 2002
DHHS (NIOSH) Publication No. 2003-111 (2002)
The sixth of a series, the Work-Related Lung Disease (WoRLD) Surveillance Report 2002
provides information on various work-related respiratory diseases and associated
exposures in the United States. The WoRLD Surveillance Report 2002 describes where
these diseases are occurring (by industry and geographic location), who is affected
(by race, gender, age, and occupation), how frequently they occur, and temporal trends.
- Section 13. Lung Cancer
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