On this page:
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 occupation.
Millions of U.S. workers are exposed to substances that have tested as carcinogens
in animal studies.
Less than 2% of chemicals in commerce have been tested for carcinogenicity.
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
- personal characteristics such as age, sex, and race
- family history of cancer
- diet and personal habits such as cigarette smoking and alcohol consumption,
- the presence of certain medical conditions,
- exposure to cancer-causing agents in the environment, and
- exposure to cancer-causing agents in the workplace.
In many cases, these factors may act together or in sequence to cause cancer.
Return to top
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 scenario.
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 cancer.
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
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 1970's.
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
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
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 employees.
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
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.
Return to top
NIOSH Carcinogen List
International Agency for Research on Cancer
National Toxicology Program
Annual Report on Carcinogen
NIOSH Pocket Guide
Respiratory Disease Surveillance (ORDS)
Lung Disease Surveillance Report 2002
Return to top