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Cancer Facts

General Cancer Facts

Cancer Causes

Environmental Exposures

Cancer Clusters

Cancer Investigations


General Cancer Facts

Unfortunately, cancer is an extremely common disease. It is estimated that one of every three people will develop some sort of cancer during their lifetime.

Cancer risk is related to age. Over 50% of cancers occur in people over age 65. As the average age of our population increases due to public health efforts and medical health advances, we can expect to see more cases of cancer. This also means that as we ourselves age, we will notice more cases of cancer in our peer groups. This also means that retirement communities will have a high number of cancers.

Cancer is not one disease but a group of more than 100 diseases characterized by an uncontrolled growth of abnormal cells. When evaluating cancer clusters and potential exposures, each cancer site or system is considered a separate disease.


Cancer Causes

Cancers have many different causes--some of which are specific and known, like smoking
and lung cancer, and many of which are unknown. Eighty percent of breast cancers have no known cause. It is a combination of factors (individual behavior, genetic predisposition, environmental factors) that determines whether or not a person develops cancer.

Most cancers diagnosed today result from exposures and events that occurred many years ago. The majority of cancers do not develop immediately after an exposure to a carcinogen, or cancer causing substance. For adults, the lag time is often 10-30 years between exposure and diagnosis. And people are highly mobile. It is likely that a person changes residence and/or jobs a number of times between exposure and development of cancer. This means identifying the cause of a person?s cancer can be very difficult.


Environmental Exposures

Cancer investigations in occupational settings have led to identification of cancer causing chemicals, or carcinogens, i.e. lung cancer in asbestos workers. These workers are frequently exposed to high doses of a carcinogen over a lifetime work history. Although environmental exposures to chemical and biologic carcinogens are a risk factor for cancers, particularly in industrial work settings, it is currently believed that these exposures contribute to a relatively small proportion of all cancer diagnoses. Only a few of the thousands of community investigations have been traced to an environmental contamination.

The majority of known cancer causes are related to lifestyle factors or personal behaviors. Some are behaviors people choose, like tobacco use and diet. Some are factors beyond control, like age and a family history of cancer.


Cancer Clusters

A cluster is the occurrence of a greater than expected number of cancers within a community-defined by geographic area, time period, worksite, etc. Some cancer clusters are random occurrences with unrelated exposures.

These types of clusters happen by chance.

However, some cancer clusters are due to a common exposure. These clusters are of concern because the cause needs to be identified and eliminated.

Some factors may indicate that a suspected cluster is due to a common exposure. For instance, clusters involving only one type of cancer, clusters involving a rare cancer, or clusters involving age groups not usually affected by the specific cancer may indicate a common source.

Get more information on cancer clusters.


Cancer Investigations

For a variety of reasons, the majority of suspected cancer clusters do not appear to be due to a common cause. Many times the numbers of confirmed cancers are not higher than expected. Sometimes the information on potential cases is incomplete and evaluation of the situation is impossible. Other times the number of cases is so small that the standard statistical methods used cannot generate valid rates. And sometimes a cluster can be shown mathematically, but no reason can be found. This may be due to limitations in knowledge about level of exposure, the frequency of migration of individuals from one community to another, or other limitations in current scientific knowledge.

The conclusion of an investigation is not always satisfying to those concerned. But as cancer surveillance and analysis occur on local, national, and international levels, health researchers will continue to find answers to the countless questions. Learn more.

For more information, please contact oscar.ohd@state.or.us.