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General Cancer Facts

Cancer Causes

Environmental Exposures


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

Individual risk factors are known to cause or contribute to many different types of cancer. Some individual risk factors cannot be changed, such as age and family history or cancer. Others are related to lifestyle issues such as poor diet, lack of exercise, exposure to tobacco, and alcohol use.


Most of what is known about cancers associated with toxic exposures in humans comes from studies of exposures to cancer-causing materials in the workplace. Workplace exposures may occur over a lifetime work history. When multiple studies show that workers with certain exposures are more likely to develop a specific type of cancer, it indicates that those exposures may cause that cancer. One example is the development of a specific type of lung cancer (mesothelioma) among asbestos workers.


Scientific studies in a work setting are complex and may take several years to complete. Reaching any definitive conclusion may be difficult, even when a specific contaminant is suspected of causing disease. The complexity is even greater when there is no specific contaminant suspected and the disease being studied is rare. Studies designed to discover an unknown cause of cancer often require data from several different states. A multi-state study ensures there will be enough information about potential contaminants and the cancer of interest to use the most appropriate study methods.


Outside the workplace setting, establishing a connection between an environmental exposure and the occurrence of cancer is even more challenging. For instance, it is often difficult to determine the amount and duration of exposure of any individual to a contaminant of concern. In addition, certain carcinogens may increase the risk of cancer, but cause relatively few cases of cancer in the community compared to other causes of the same cancer. Between 1990 and 2011 over 400 health department investigations of apparent community cancer clusters were conducted. Only one of those investigations identified a cancer-causing agent (asbestos).


For more information on Responding to Cancer Cluster Inquiries