Cancer cluster

Overview
Cancer cluster is a term used by epidemiologists, statisticians, and public health workers to define an occurrence of a greater-than-expected number of cancer cases within a group of people in a geographic area over a period of time.

Historical examples of work-related cancer clusters are well documented in the medical literature. Notable examples include: scrotal cancer among chimney sweeps in 18th century London, osteosarcoma among female watch dial painters in the 20th century, skin cancer in farmers, bladder cancer in dye workers exposed to aniline compounds, and leukemia and lymphoma in chemical workers exposed to benzene.

Cancer cluster suspicions usually arise when members of the general public report that their family members, friends, neighbors, or coworkers have been diagnosed with the same or related cancers. State or local health departments will investigate the possibility of a cancer cluster when a claim is filed. In order to justify investigating such claims, health departments conduct a preliminary review. Data will be collected and verified regarding: the types of cancer reported, numbers of cases, geographic area of the cases, and the patients clinical history. At this point, a committee of medical professionals will examine the data and determine whether or not an investigation (often lengthy and expensive) is justified.

In the U.S., state and local health departments respond to more than 1,000 inquiries about suspected cancer clusters each year. It is possible that a suspected cancer cluster may be due to chance alone, however, only clusters that have a disease rate that is statistically significantly greater than the disease rate of the general population are investigated. Given the number of inquiries it is likely that even some of these are due to chance alone.

A cluster is more likely to be "genuine" if the case consists of one type of cancer, a rare type of cancer, or a type of cancer that is not usually found in a certain age group. Between 5% to 15% of suspected cancer clusters are statistically significant.

Related chapters

 * Biostatistics
 * Incidence
 * List of cancer clusters
 * Risk assessment
 * Toxicology

Resources

 * Cancer Mortality Maps & Graphs: U.S., 1950-94
 * National Institute of Environmental Health Sciences (NIEHS)
 * U.S. Centers for Disease Control
 * U.S. Environmental Protection Agency
 * Australian Story about a cluster of breast cancer cases in the workplace