Cancer cluster is the term used when we observe several cancer cases among persons living in the same area, whose cancer has been caused, at least in part, by an environmental risk factor that they all share. Epidemiologists have determined that a group of cases is more likely to be a true cluster if it involves: A large number of cases of one type of cancer, rather than several different types; A rare type of cancer, rather than common types; An increased number of cases of a type of cancer in an age group not usually affected; An exposure common to all the cases that has potential to cause cancer.

The occurrence of a larger-than-expected number of cases of cancer within a group of people in a geographic area over a period of time.

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.