Medically Reviewed by Karim Tazi, MD

In the 1960s, researchers identified one of the first major “cancer clusters.” Workers, who came in contact with asbestos, reported a high rate of mesothelioma (which you may have heard about through TV commercials). Mesothelioma is rare form of cancer of the lining of the lung or abdomen. Since then, when a number of cancer cases arise in one family or community, the term “cancer cluster” comes up.

“The truth is that an actual cancer cluster is rare for a number of reasons,” says McLeod Oncologist Dr. Karim Tazi. “A formal cancer cluster must have several distinctive characteristics: all the cancers must involve the same type of cancer; it must occur in a carefully defined group of people (same race/ethnicity or gender); it must appear in a defined geographic area and over a specific period of time.”

WHY IT’S PROBABLY NOT A CANCER CLUSTER
Everyone knows a number of people who have cancer, because half of all men and a third of all women will have cancer in their lifetime. Millions of new cases are diagnosed every year. In the end, cancer touches 2 out of 3 families.

You’re likely to know one or more people with one of the most common cancers – lung, colon, prostate in men, or breast in women. These cancers account for 50 percent of all cancers in this country.

Actual clusters, though, most likely involve rarer cancers, such as brain or bladder cancer or leukemia. An environmental element is usually involved, such as those workers exposed daily to asbestos or a community exposed to tainted water.

In 80 percent of the cases of suspected cancer clusters, it turns out NOT to be a true cluster, because:

• Cancers are within the same family. Colon and breast cancer sometime follow family lines.
• Cancers are not related to one another.
• They are the type of cancers found commonly among people of the same age or sex.
• People with cancer are not in the same place.

WHY WE THINK IT MIGHT BE A CLUSTER
We are likely to know a number of people with cancer. A “suspected” cluster occasionally involves what scientists call “selective perception.” If you know one person with cancer, you tend to notice other people with cancer.

It’s similar to buying a new car. If you buy a certain make and color, you tend to drive it and think, “Wow, look at all those people in the same kind of car I have.”

Remember though, there are specific characteristics that must be present to meet the definition.

ACTION YOU CAN TAKE
If you believe a situation fits the definition of a cancer cluster, you can go to the SC Department of Health & Environmental Control for more information and contacts.

Have a cancer question?  Ask a Cancer Specialist.

Sources: McLeod Health, South Carolina Department of Health & Environmental Control, Centers for Disease Control and Prevention, Cancer Research UK, American Cancer Society