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Environmental Health: Cancer and Cancer Clusters

Find answers on this page to frequently asked questions about cancer and cancer clusters.

Cancer develops when the deoxyribonucleic acid (DNA) of a cell is damaged causing mutations. These mutations cause a cell to grow out of control, becoming cancer.

There are more than 100 different types of cancer. Some cancers are more common than others. Each type of cancer has its own causes and chances for survival. Many of those causes are still unknown. No one should assume that all types of cancer in a neighborhood or community share a common cause.

Cancer is the second leading cause of death in the United States, following heart disease. According to the American Cancer Society, about 30% of Americans will develop cancer at some point in their lives—affecting three out of every four families. Given these statistics, it’s not surprising to know several people in a neighborhood or workplace who have cancer.

Cancer can develop in people of all ages, but the likelihood of developing the disease rises sharply in people over 45 years old. In fact, 77% of all cases of cancer are in people over the age of 55. Age is the single biggest risk factor for cancer.

The causes of most cancers are not well understood. Scientists know that many cancers are influenced by a combination of factors, such as the environment, heredity, and lifestyle.

Known cancer risk factors include:

  • Getting older
  • Lifestyle factors, including using tobacco (such as smoking or chewing tobacco), consuming more than two alcoholic beverages per day, and being exposed to sunlight or tanning beds. Poor nutrition, obesity, and lack of physical activity also are believed to be important risk factors
  • A family history of cancer
  • Infection with certain viruses, bacteria, or fungi. For example, hepatitis B, human immunodeficiency virus (HIV), or human papillomavirus (HPV)
  • Environmental factors such as radon, arsenic in drinking water, asbestos, air pollution, and exposure to certain chemicals, either at home or at work
  • Chronic inflammation
  • Hormonal factors like long-term exposure to oxygen

Many people believe that cancer is usually caused by exposure to toxic substances in the environment. However, most cancers are affected by lifestyle factors.

The exact impact of environmental pollutants on cancer development is not known, but estimates suggest less than 10% of cancers are related to environmental factors.

Cancer does not develop immediately after you’ve had contact with a cancer-causing substance, or carcinogen.

Often, it takes a long period of time, such as 15 to 30 years, before cancer is diagnosed after exposure to a carcinogen. This makes tracking what caused the cancer very difficult. Also, since people are exposed to so many substances every day, it is very difficult to determine which ones may have increased their risk for cancer.

A cancer cluster is an unusual number of people who live in the same area or work in the same place developing the same type of cancer within a certain window of time.

Cancer clusters are very rare. To date, the Wisconsin Department of Health Services (DHS) hasn’t identified a cancer cluster caused by environmental factors in the state. However, it is not uncommon for people to suspect that cancer cases in their neighborhood or workplace are related to some toxic substance in the environment.

Even if an unusual number of people who live or work in the same place develop the same cancer type, you should not assume the cause is exposure to an environmental carcinogen. It may have simply occurred by chance or due to a common lifestyle behavior, like smoking.

One of the reasons that cancer clusters are hard to track is because people move. For example, in the 1990 census, more that 50% of people reported living somewhere else five years earlier.

DHS is actively working with the Wisconsin Cancer Registry, hospitals and other agencies to track cancer rates and locations, promote cancer prevention behaviors, and investigate cancer causes.

DHS and other organizations are committed to promoting cancer prevention behaviors and cancer screening while investigating other possible causes of cancer.

We ask people to report evidence of environmental contamination to the Wisconsin Department of Natural Resources so they can take appropriate action.

More resources

Who to contact for help

If you have health-related questions, contact:

DHS Division of Public Health
Bureau of Environmental and Occupational Health
PO Box 2659 Madison, WI 53701-2659

You can also email

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Last revised June 21, 2023