Identifying Cancer Clusters

Is the number of cancer diagnoses creeping up where you live? Is it just by chance? Or could an environmental toxin be lurking in the water, soil or air? Find out what you need to know about getting a cancer cluster investigated.

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One of the first questions people faced with a cancer diagnosis ask is, "What caused this?", especially when it strikes young children who don't typically get cancer. Sometimes you learn why; a DNA defect could foreshadow certain types of colon cancer for instance, or an unhealthy behavior such as smoking jacked up your risk. But it could also be something lurking in the environment, a carcinogen that has entered the water supply, soil or the air where we live, work, play or attend school.

Government agencies track the number and type of cancers that typically occur, so they have a pretty good idea of what to expect in a given group of people every year. So when the number of cancer diagnoses in a community creeps up inexplicably, a red flag goes up and a cancer cluster is suspected.

But before the government gets wind of this suspicion, it has to be reported. And that is usually the result of a hunch: A mother learns her son has a rare brain tumor and a few miles cross-town she hears there is another case; or coworkers at a plant are struck down with the same rare cancer.

While an up in cancer cases could be a random occurrence, it may also be caused by an outside source. Getting to that source takes a perceptive eye, coupled with the tenacity of a group of people, the expertise of medical professionals, and the willingness of government agencies to intervene and investigate it fully.

Famous Cancer Clusters

One notable cancer cluster was discovered in the early 1900s when a group of watch-dial workers began to mysteriously die from cancer. The workers, who would lick the tips of their brushes so that they could more easily apply the radium paint that illuminated the watch hands, were unknowingly exposing themselves to radioactive material. The radium poisoning eventually caused a host of complications including, cancer of the jawbone.

Another well-known cancer cluster was discovered in Woburn, MA when a clergyman noticed that over a 15-year period an unusual amount of kids in his town were getting childhood leukemia. The investigation and court cases became a bestselling book and movie, A Civil Action .

And most of us know about the cancer cluster breakthrough that came from the suspicions of Erin Brockovich, the feisty Californian whose unrelenting investigation lead to the source of chromium poisoning her town's drinking water.

These, and other noteworthy investigations, have saved the lives of future generations. The source was identified, the contributors were made accountable, and the toxins were removed from the environment.

Sadly though, 75% of investigations come up empty-handed or are dismissed. Still, finding the source of a cancer cluster is important because it can not only save lives but also add to a growing list of environmental toxins that humans should avoid.

What Constitutes a Cancer Cluster?

Vital information about the causes of cancer can come from a branch of science called epidemiology, the study of factors that cause disease. Epidemiologists working for a state's public health department are charged with investigating an average of 1,000 suspected cancer clusters every year. 

It is a complicated process but put simply, they look at the number of cancer cases in a defined geographic area, over a defined period of time, in a defined group of people and compare it to what they might normally expect to diagnose in a group of that size. If the number of cases exceeds the number they normally expect in a statistically meaningful amount, it can signal a cancer cluster.

The cancer is usually, although not always, one type. It is oftentimes rare, and the age at onset may be unusual for that cancer type. If a carcinogen is identified it is be measured to see if it exceeds acceptable environmental limits.

This is not a perfect system and there are many experts who deny the validity of  cancer cluster investigation. The science is imperfect: Cancer can take years to develop and can be masked by unhealthy behaviors; people can get lost to follow-up, die of other causes, or move away. And some people may be exposed to cancer causing substances but have a genetic make-up that reduces their susceptibility to the harms of the carcinogen. All of these things can affect the results, leaving community members to wonder if they will ever get a real answer. Many times, they do not.

What Can the Community Do?

There was a time when people who were diagnosed with cancer didn't discuss it much with their neighbors, coworkers or authorities. Today, people are more inclined to speak up, ask questions and do research on their own and that can only help to get an investigation underway.

To learn more about cancer clusters in your community and to protect you and your loved ones, follow Dr. Oz's advice.

Key resources about cancer clusters can be found at the Centers for Disease Control and Prevention's National Center for Environmental Health and the National Program of Cancer Registries .