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Cancer Facts and Cancer Clusters

Below you will find answers to frequently asked questions about cancer and cancer clusters.

Cancer is a group of more than 100 different diseases characterized by uncontrolled growth and spread of abnormal cells. Each type of cancer has a different rate of occurrence, causes, and chances for survival. Therefore, 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 now living will eventually develop cancer. Over the years, cancer will strike about three out of four families. Given these statistics, it is not surprising to know several people in a neighborhood or workplace who have cancer.

While cancer occurs in people of all ages, cancer rates rise sharply among people over 45 years of age. In communities where the majority of residents are over 60 years of age, scientists would expect more cancer than in a neighborhood of mixed ages.

The causes of most cancers are not well understood. Scientists know that many cancers are influenced by a combination of factors, including the environment, heredity, and behaviors related to how we live, called lifestyle behaviors. Lifestyle behaviors that increase cancer risk include:

  • Tobacco use, such as smoking or chewing tobacco
  • Drinking more than two alcoholic beverages per day
  • Nutrition – a diet lacking fresh fruits, vegetables and whole grains
  • Obesity
  • Physical inactivity
  • Excessive exposure to sunlight

Other factors that can increase a persons cancer risk are a family history of cancer, certain infectious diseases (e.g., hepatitis B, human immunodeficiency virus (HIV), human papillomavirus (HPV)) and hormonal factors (for women, high cumulative exposure to estrogen). Finally, work exposure to some chemicals increases the risk for certain cancers.

Many people believe that cancer is usually caused by exposure to toxic substances in the environment. However, most cancers are affected by lifestyle factors. It is not known the exact impact of environmental pollutants on cancer development, but estimates suggest less than 10% of cancers are related to environmental factors.

Cancer does not develop immediately after contact with a cancer-causing agent. Often there is a long time period, such as 15 to 30 years, between the exposure to a carcinogen (a cancer-causing substance) and medical diagnosis of cancer. This makes it very difficult to track what caused the cancer. Cancers are usually related to long-term lifestyle factors (like smoking) or significant exposure to a carcinogen for many years.

A cancer cluster is an unusual number of the same type of cancers occurring over a given time among people who live in the same geographical area or workplace. The concern that a cancer cluster may exist usually occurs when someone's spouse, neighbor, or friend is diagnosed with cancer. This often brings an awareness of others who have any type of cancer and a desire to answer the question, "Why?"

To date, the Department of Health Services (DHS) has not identified an environmentally caused cancer cluster in Wisconsin. It is not uncommon for people to suspect that the cause of all cancers is some toxic substance in the environment or workplace.

Even if there is an unusual number of a certain cancers in a community, it shouldn't be assumed the cluster was caused by exposure to an environmental carcinogen. This cluster may have occurred simply by chance or from unrelated causes-- such as smoking. It is hard to investigate a cancer cluster and track past environmental exposures because people often change their residence. For example in the 1990 census, over 50% of people reported living somewhere else five years ago.

DHS, hospitals, and other agencies are actively tracking cancer rates and locations. Health professionals at DHS and other organizations are committed to promoting cancer prevention behaviors, while investigating other possible causes of cancer. The public should also continue to report environmental contamination to the Department of Natural Resources for appropriate action.

For more information (including what you can do to prevent cancer)

For health-related questions, contact the Division of Public Health, Bureau of Environmental and Occupational Health,
PO Box 2659, Madison, WI 53701-2659. Telephone: 608-266-1120.

Back to Environmental Health Resources

Last revised January 5, 2023