Epidemiology and Cancer Clusters

Epidemiology is the study of the factors that cause illnesses and disease with in a population. This field of study is critical in the prevention and spread of communicable and non-communicable disease. Epidemiology is used to identify disease from the outbreak through diagnosis and treatment.

Epidemiolgists, those scientists who study the causes of disease, utilize knowledge in biology, sociology and philosophy in an effort to understand and communicate risk factors for disease.

Carcinogenesis, or the process by which normal cells become cancer cells, is studied by epidemiologists to determine the existence of cancer clusters.

Cancer clusters are rare and epidemiologists determine, through specific criteria if and when a cancer cluster exists. Many individuals will report a cancer cluster but it is the job of an epidemiologist to determine if there is an environmental cause for the incidence of cancer or if the high rate of cancer is merely coincidence.

An epidemiologist will utilize several specific criteria to decide if further investigation is necessary in regards to a cancer cluster. When one type of cancer is found in a population in large numbers this may be a warning sign of a cancer cluster. There are over 100 varieties of the disease so it is rare for one, specific type to be found in large numbers in a population.

There are rare forms of cancer and there are more common forms of the disease. If a rare form of cancer is found in high numbers within a community or group this may also signify a cancer cluster.

A third warning sign to the existence of a possible cancer cluster is when a specific age group in an area suffers from a form of cancer that does not usually affect that age group.

In the beginning stages of determining the existence of a cancer cluster, epidemiologists must first assess the health of the individuals affected. If the cancer is a result of an underlying infection or due to the spread of cancer from another area of the body, this individual is not part of a cancer cluster. The primary cancer is the only cancer considered in the study of a cancer cluster.

Epidemiologists will use biological knowledge to study the significance and causes of the particular type of cancer. The scientist will use knowledge of biological causes of disease to determine if exposure to environmental factors has the ability to cause the specific type of cancer.

In the process of deciding whether or not a cancer cluster truly exists it is important for the epidemiologist to define the borders of the geographical area. Often there are cases in outlying areas causing additional individuals to become involved in the study. These situations may create false cancer clusters.

It is very difficult to determine with absolute certainty if the number of cancer cases is higher that what would be normally expected. The use of statistical factors such as age, gender and race are utilized but lifestyle factors may cause the numbers to be different than what would normally be expected.

It is not possible in all cases to make a determination that a cancer cluster does exist. In some situations the cases of cancer are higher than what would normally be expected within the geographical area in the specified time period, however the epidemiologists cannot find an underlying cause for the disease.

In some situations the study of a cancer cluster cannot be completed due to the small amount of subject cases. The epidemiologist must have enough cases of the disease to provide accurate conclusions.

Even in situations when there are many cases, the history of the individuals involved may make specific determinations regarding exposure impossible. For example, an individual may have lived in many areas over the course of a lifetime and determining when and where exposure occurred would then be impossible.


Factors Affecting Cancer Rates

The age of a group of individuals will affect the rate of cancer development. Individuals over the age of 45 have a much greater risk of developing cancer than people younger than 45 years of age. Men and women over the age of 60 have an even greater risk of developing some form of cancer. It would stand to reason that these age groups would have more cases of cancer than other groups in younger age brackets.

Other factors that may affect the rates of cancer development in a particular group are lifestyle behaviors. Individuals with a poor diet may experience a higher cancer rate than those who eat healthfully. A diet rich in vegetables, fruit, lean meats and fish and healthy fats can help prevent cancer in some individuals.

Exercise is also an important part of keeping cancer at bay. Individuals who do not participate in any regular form of exercise are at a greater risk for developing cancer. According to the American Cancer Society one third of all cancer deaths are in some way related to nutrition, obesity, and/or physical inactivity, and could possibly be prevented.

In one study conducted by Dr. Christine Friedenreich, of Alberta Health Services-Alberta Cancer Board in Calgary, Canada, it was discovered that women with breast cancer who had exercised more than four hours per week over their lifetime had a 44 percent lower risk of dying from the disease. Other studies have found similar results with other forms of the disease.

“Greater participation in physical activity has consistently been associated with reduced risk of cancer incidence at several sites, including breast and colon cancers,” said James McClain, Ph.D., cancer prevention fellow at the National Cancer Institute.

Another enormously risky lifestyle behavior is tobacco usage. It is estimated that discontinuing the use of tobacco could prevent one third of all cancers.

These lifestyle factors may cause the incidence of cancer to increase in certain groups such as families or employees that participate in these high-risk behaviors. Cancer clusters may seem to exist however it is lifestyle behaviors, not external environmental carcinogens that cause the unusually high incidence of cancer in these groups.