Identification
The investigators develop a "case" definition, a time period of concern, and the population at risk. They then calculate the expected number of cases and compare them to the observed number. A cluster is confirmed when the observed/expected ratio is greater than 1.0, and the difference is statistically significant. Usually, a local or state health department provides the first response to a suspected cancer cluster. The local or state health department gathers information about the suspected cancer cluster (e.g., types of cancer, number of cases, addresses and occupations of those people with cancer, possible causes), develops and applies the case definition, and determines whether there is a greater-than-expected number of cases.Interpretation
Confirmation of a cancer cluster does not necessarily mean that there is any single, external cause or hazard that can be addressed. A confirmed cancer cluster could be the result of any of the following:- chance
- miscalculation of the expected number of cancer cases (e.g., not considering a risk factor within the population at risk)
- differences in the case definition between observed cases and expected cases
- known causes of cancer (e.g., smoking)
- unknown cause(s) of cancer.
Prevention and early detection
Concern about cancer and cancer clusters provides an opportunity for people to learn about how they can prevent cancer or identify it early. Sixty-five percent of public inquiries about cancer clusters involve cancers for which screening and preventive measures exist. The best steps that people can take regarding cancer are to (1) educate themselves about their personal risk and risk factors for cancer, (2) avoid these risks, and (3) take advantage of recommended cancer screenings.(published with permission in writing from:http://www.cdc.gov/)


