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South Carolina Central Cancer Registry

Cancer Clusters

What is a cancer cluster?

A cancer cluster is a group of more cancer cases than normal in a small area like a neighborhood, or cases occurring within a short time period.  Perceived or suspected cancer clusters are reported when people learn that an unusual number of their friends, family, neighbors, or co-workers have cancer or have died of cancer.

It is normal to know a lot of people with cancer. The American Cancer Society (ACS) estimates that 1 in 2 men and 1 in 3 women will have cancer in his or her lifetime, and it will affect 2 in 3 families.

At least five types of cancer are very common:

  • Lung and colon cancer in men and women
  • Breast and uterine cancer in women
  • Prostate cancer in men

These five major cancers make up over 70 percent of all the cancer cases in the United States today. Because these five cancers are so common, several cases might occur in one place. Cancer clusters might include these, but they are more likely to involve rarer types of cancer.

A true cancer cluster exists when the number of cancer cases that occur is statistically significantly more than would be expected by chance alone in a certain location or time period. This is most often true for rarer cancers, like bladder, leukemia, or brain cancer.  However, there may be no common thread can be found among the cases, such as working at the same plant for many years, or living in the same neighborhood where a common exposure could have occurred.

A meaningful cancer cluster is a true cluster where there are common threads that link the cases in some way and that meet other scientific criteria or rules of thumb, such as evidence of at least a 3-fold increase in the number of cases of a particular kind of cancer over the number expected

How are community cancer assessments conducted?

In response to a community cancer inquiry, the SCCCR conducts a Community Cancer Assessment (CCA) for that community. A CCA is a summary of the observed numbers of new cancer cases and deaths in a ZIP Code for the last five years of available data, compared to the expected numbers of cancer cases and deaths in a particular ZIP Code (the numbers that might be expected if the ZIP Code had the same cancer incidence and mortality rates as the state of SC). The ZIP Code area is the smallest area that can be analyzed (due to the need for stable population counts). This comparison helps to determine if the number of reported cases and deaths is above normal. The SCCCR provides approximately 40-50 CCAs by special request each year.


If any statistical excesses exist, additional examination is performed to determine if a true cancer cluster exists.  However, over 95 percent of reports are not true clusters. They appear to be clusters because cancer is so common.  Even a true cluster can occur randomly and may not be a meaningful cancer cluster (resulting from one common factor). Chance alone can sometimes account for higher rates of cancer.   Since the SCCCR began investigating community cancer inquiries in 1996, only one true cancer cluster has been identified in South Carolina.  A CCA report for any SC ZIP Code is available upon request.

View the SCCCR's Protocol for Handling Cancer Cluster Investigations (PDF-1,274KB)

View the SCCCR's Cancer Cluster Guideline Summary (PDF - 14KB)


Cancer Cluster Factsheets