Cancer Awareness Cancer Awareness Cancer Awareness Cancer Awareness

Understanding cancer clusters

Each year, more than 1,000 suspected cancer clusters are reported to state departments across the United States. Not exclusive to the U.S., cancer clusters can occur anywhere, and notable cancer clusters throughout history have included a scrotal cancer cluster among 18th century chimney sweeps in London, skin cancer clusters in farmers and a leukemia cluster in Massachusetts that inspired the book and film A Civil Action.

As notable as such cases have been, cancer clusters remain somewhat of a mystery to the general public. Scientists who study cancer clusters, which many define as a greater number of cancer cases than would be expected in a defined geographic area or group of people over a certain period of time, do so in an effort to identify areas of increased risk and in an attempt to determine what might be causing that increased risk. When newsworthy cancer clusters make headlines or even make it to Hollywood, some common questions typically arise.

What makes a cancer cluster a cluster?

Cancer is a relatively broad term, referring to a group of more than 100 diseases, each with its own characteristics. In general, a cancer cluster involves one rare type of cancer. However, a cancer cluster can also occur whenever there are larger than expected numbers of a more common type of cancer. In addition, a cancer cluster can also occur when a certain group of people gets a certain type of cancer that is not typical among their group, such as a group of children getting a cancer that's more common among adults.

These distinctions are important because cancer is so common. According to the American Cancer Society, nearly half of all men and slightly more than one-third of all women will develop cancer during their lifetimes. So it's entirely plausible that a number of people within a small geographic area will develop cancer at roughly the same time. However, unless cancer cluster characteristics are applicable, then these cases of cancer are likely not a cluster, but more likely a byproduct of cancer's prevalence.

Where is exposure most common?

The ACS notes that most well-documented cancer clusters that are caused by a shared exposure are not found in the community where people live. Instead, these clusters are more often found in the workplace. That's because exposure to certain chemicals or other risk factors for cancer tend to be higher in the workplace than at home or in a community. What's more, it's easier to trace the people being exposed in a workplace group than it is in an entire community.

How often are suspected cancer clusters actually deemed clusters?

As mentioned earlier, the U.S. alone has more than 1,000 suspected clusters reported to its state departments every year. Once a suspected cluster is reported, an investigation will be conducted. In the U.S., as many as 80 percent of these investigations conclude that a suspected cluster is not actually a cancer cluster. During an investigation, a host of factors are considered, including the types of numbers of cancers involved, any suspected exposures that might cause cancer, and the area and time period in which the cases occurred. Specifics as to each person thought to be affected and about the cancers themselves also help investigators determine if a suspected cluster is actually a cluster.

Each year, thousands of suspected cancer clusters are reported across the globe. Gaining a better understanding of cancer clusters can help calm any initial distress until enough research is conducted by the appropriate authorities to determine if a suspected cluster is actually a cluster.