What is a cancer cluster?
A cancer cluster is defined as a greater than expected number of cancer cases that occurs within a group of people, in a geographic area, or over a period of time. A person may suspect that a cancer cluster exists when several loved ones, neighbors, or coworkers are diagnosed with cancer. However, what appears to be a cluster may actually reflect the expected number of cancer cases within the group or area. When considering the possible existence of a cancer cluster in your area, it is important to remember a few key facts: 1) cancer is a common disease, affecting about one in four people in their lifetime; 2) the term cancer refers not to a single disease, but instead to a group of related yet different diseases; 3) a cancer cluster may be due to chance alone, like the clustering of balls on a pool table; and 4) an apparent cancer cluster is more likely to be genuine if the cases consist of one type of cancer, a rare type of cancer, or a type of cancer that is not usually found in an age group.
How do I report a suspected cancer cluster or obtain information on cancer statistics or trends for my area?
Contact your local or state health department or state cancer registry.
These agencies provide the first level of response and have the most
current local data. Contact your local or state health department through
http://www.cdc.gov/nceh/clusters/
statelocal.htm. Contact your state cancer registry through
http://apps.nccd.cdc.gov/cancercontacts/npcr/contacts.asp.
Who responds to inquiries about a suspected cancer cluster?
Local or state health departments, along with cancer registries, provide the first level of response and have the most current local data for the area. If needed, these agencies can request assistance from federal agencies, including
- CDC
- National Center for Environmental Health (NCEH):
http://www.cdc.gov/nceh/default.htm - National Institute for Occupational Safety and Health (NIOSH):
http://www.cdc.gov/niosh/homepage.html - National Center for Chronic Disease Prevention and Health
Promotion (NCCDPHP):
http://www.cdc.gov/nccdphp/
- National Center for Environmental Health (NCEH):
- Agency for Toxic Substances and Disease Registry (ATSDR):
http://www.atsdr.cdc.gov/
- U.S. Environmental Protection Agency (EPA):
http://www.epa.gov/ [external link]
When people contact CDC with concerns about a suspected cancer cluster, CDC provides information and refers them to the appropriate local or state health department or cancer registry.
How are suspected cancer clusters investigated?
State and local health departments respond to cancer cluster reports
and inquiries about suspected clusters. A CDC survey
(http://www.cdc.gov/nceh/clusters/status.htm)
revealed that most state health departments’ strategies for cluster
response are based on CDC’s “Guidelines for Investigating Clusters of
Health Events” (http://www.cdc.gov/mmwr/preview/mmwrhtml/
00001797.htm) with some modifications. Usually, a local or state
health department starts by gathering information about the suspected
cancer cluster including expected cancer rate, types of cancer, number of
cases, and the age, sex, race, address, occupation, and age at diagnosis
of the individuals with cancer. Information may be verified by contacting
patients and relatives or by obtaining medical records. This information
is then compared to census data and state cancer registry data to
determine if there is a higher than expected number of cases. Most
investigations do not proceed beyond evaluation of the gathered
information; however the local or state health department may perform a
more intensive assessment or comprehensive epidemiological study. The
decision to proceed to a more intensive investigation is usually based on
a set of rules developed by the health department.
What challenges regarding suspected cancer clusters do investigators face?
Cancer cluster investigations are complex and difficult for several reasons. Although any cancer case is one too many, suspected cancer clusters often do not contain enough cases for investigators to do a meaningful statistical analysis or reach a conclusion. Investigators must choose the appropriate comparison population and decide how to handle cases that move in or out of the area. Determining the cause of cancer is complicated because exposure to cancer-causing agents may have occurred many years before diagnosis. Therefore, assessing the amount and type of cancer-causing agents an individual has been exposed to is difficult. Unfortunately, cancer is often the result of a combination of agents and risk factors that interact in a way that science does not yet fully understand.
How do I find out if a suspected cancer cluster is being investigated in my area? How do I find information on an investigation in my area?
Contact your state cancer registry or your local or state health department. Contact your state cancer registry through http://apps.nccd.cdc.gov/cancercontacts/npcr/contacts.asp or your local or state health department through http://www.cdc.gov/other.htm#states. For information about public health assessments conducted by ATSDR, search by state at http://www.atsdr.cdc.gov/HAC/PHA/. For information on CDC investigations, go to http://www.cdc.gov/nceh/clusters/investigations.htm.
What can I do to reduce my risk of developing cancer?
Adopt a healthy lifestyle that includes avoiding tobacco use, excessive alcohol consumption, and sun exposure. Increasing physical activity, maintaining a recommended body weight, eating a healthful and nutritious diet, and taking advantage of cancer screening also will reduce your risk.
For more information about preventing cancer, visit
- The National Institute of Health’s National Cancer Institute:
http://www.cancer.gov/cancerinfo/ - American Cancer Society:
http://www.cancer.org/docroot/home/index.asp - CDC’s Cancer Prevention and Control Program:
http://www.cdc.gov/cancer/.
Where can I find more information about cancer clusters?
For links to resources about cancer clusters in general, as well as information about cancer registries and publications on cancer clusters, visit http://www.cdc.gov/nceh/clusters/links.htm.
For an extensive overview of cancer clusters, including facts about cancer, the environment, and heredity; methods used in investigating suspected cancer clusters; guidelines for reporting suspected cancer clusters; and a list of additional resources, visit the NCI’s Cancer Cluster Web site at http://cis.nci.nih.gov/fact/3_58.htm [external link].
NCI has also collaborated with the National Institute for Environmental Health Sciences to publish Cancer and the Environment: What You Need to Know, What You Can Do [external link] [PDF, 615 Kb]. This booklet addresses concerns about the connection between cancer and exposure to toxic substances in the environment. It contains information about which types of substances are either known to cause or likely to cause cancer, and what can be done to reduce exposures to them. It also explains how scientists discover which substances are likely to cause cancer. The booklet provides an extensive overview of environmental causes of or risk factors for cancer including lifestyle factors such as diet and physical inactivity, certain medical drugs, hormones, radiation, viruses, bacteria, and environmental chemicals that may be present in the air, water, food, and workplace.