Cancer clusters

Definition

A cancer cluster is defined as a greater-than-expected number of cancer cases that occurs within a group of people in a geographic area over a period of time.

Challenges in identifying

The complex nature of cancer makes it inherently challenging to identify, interpret, and address cancer clusters. "Cancer" is a term representing many diseases with a variety of causes. The time between exposure to a cancer-causing agent, or the existence of other risk factors, and the development of cancer can be decades; therefore, causes are hard, and in some cases impossible, to identify. Cancer in general is common. In the U.S., 1 in 3 people will develop cancer in his or her lifetime. According to the American Cancer Society (Cancer Facts and Figures 2005), about 1,372,910 new cancer cases are expected to be diagnosed in 2005. Cancer rates vary by age, race, gender, risk-factors, and type. We know that risk for cancer increases with age and that cancer is caused by both external factors (e.g., tobacco, chemicals, radiation, and infectious organisms) and internal factors (e.g., inherited mutations, hormones, immune conditions). Nutrition, physical inactivity, obesity, and other lifestyle factors also play a role in cancer risk and outcomes. These factors may act together or in sequence to initiate or promote cancer. Ten or more years often pass between exposures or mutations and detectable cancer. Some racial and ethnic groups have a higher incidence of and deaths due to cancer. Such disparities may be due to multiple factors, such as late stage of disease at diagnosis, barriers to health care access, history of other diseases, biologic and genetic differences, health behaviors, differences in exposures to carcinogens in the environment and the workplace, and other risk factors.

Characteristics

What first appears to be a cancer cluster may not be one after all. A review of the situation may show that the number of new cancer cases is in the expected range for the population and therefore that the cases do not represent a cancer cluster. Cancer cases are more likely to represent a cancer cluster if they involve (1) one type of cancer, (2) a rare type of cancer, or (3) a type of cancer in a group read more