Cancer Clusters

A cancer cluster refers to the occurrence of a greater than expected number of cancer cases among a group of people in a defined geographic area over a specific time period. A cancer cluster may be suspected when people report that several family members, friends, neighbors, or coworkers have been diagnosed with the same or related types of cancer.

Because cancer is a relatively common disease, cases of cancer can appear to cluster even when there is no connection among them. That is, clusters of cancer can arise by chance.    

Some cancer clusters have been shown through careful investigation to be the result of a specific cancer-causing substance in the environment. However, such findings are extremely rare. One review of 576 cancer cluster investigations conducted over 20 years found that for only 72 of the apparent clusters could an increase in cancer rate be confirmed (1). Only three of the 72 clusters could be linked to a possible exposure, and in just one case was a clear cause identified.

Concerned individuals should contact their local or state health department to report a suspected cancer cluster or to find out if one is being investigated (2). Health departments provide the first response to questions about cancer clusters because they, together with state cancer registries, will have the most up-to-date data on cancer incidence in the area. The U.S. Centers for Disease Control and Prevention (CDC) website provides links to state and local health departments. These agencies may also be listed in the blue pages of government listings in telephone books.

Although potential cancer clusters are evaluated primarily by state and local health departments, states may request technical advice or assistance from several federal agencies: the CDC; the Agency for Toxic Substances and Disease Registry (ATSDR), which is part of CDC; and the Environmental Protection Agency.

Researchers at NCI and elsewhere regularly conduct surveillance studies of cancer incidence and analyze variations in those trends, including the frequency, distribution, and patterns of cancer in groups of people. These analyses can reveal patterns of cancer in specific populations and identify changes that may warrant investigation.

Several NCI resources allow users to visualize cancer trends by geographic location. For example, the NCI Cancer Atlas is a tool that allows users to create maps of cancer statistics, demographics, and risk factors. The joint NCI-CDC State Cancer Profiles website provides interactive maps to give dynamic views of cancer statistics by states and counties.

In addition to state and local health departments, the following agencies may have more information about cancer clusters.

Agency for Toxic Substances and Disease Registry (ATSDR)
Centers for Disease Control and Prevention
1–800–232–4636 (1–800–CDC–INFO)
https://www.atsdr.cdc.gov

CDC's ATSDR conducts public health assessments of potentially hazardous waste sites, performs health consultations on specific hazardous substances, designs and conducts health surveillance programs, and provides education and training about hazardous substances. Information about public health assessments conducted by ATSDR can be found on its Public Health Assessments and Health Consultations page. Reports can be searched by state or U.S. territory. Contact information for ATSDR regional offices is available online.

National Center for Environmental Health (NCEH)
Centers for Disease Control and Prevention
1–800–232–4636 (1–800–CDC–INFO)
cdcinfo@cdc.gov
https://www.cdc.gov/cancer-environment/php/guidelines/  

CDC's NCEH works to promote healthy and safe environments and prevent harmful exposures. The NCEH website includes general information about cancer clusters, links to resources, and answers to frequently asked questions.

National Institute for Occupational Safety and Health (NIOSH)
Hazard Evaluation and Technical Assistance Branch
Health Hazard Evaluation (HHE) Program
Centers for Disease Control and Prevention
513–841–4382
HHERequestHelp@cdc.gov
https://www.cdc.gov/niosh/hhe

The HHE Program of CDC's NIOSH investigates potentially hazardous working conditions, including suspected cancer clusters. Employees, authorized employee representatives, and employers can request these evaluations. HHE reports are available on the NIOSH website.