A greater-than-expected number of cancer cases that occurs within a group of people in a geographic area over a period of time. A person may expect that a cancer cluster exist 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.
