Cancer Clusters in America (Stevie JoEllie's Cancer Care Fund )

Cancer Clusters in America

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Contents

1 Definition and Overview
2 Facts About Cancer
1. 2.1 Genetics
2. 2.2 Environment
3 Reporting Suspected Cancer Clusters

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Definition and Overview

by Wilma Ariza, Thyroid Cancer Advocate

A disease cluster is the occurrence of a greater than expected number of cases of a particular disease within a group of people, a geographic area, or a period of time. Clusters of diseases have concerned scientists for centuries.

Some recent disease clusters include the initial cases of a rare type of pneumonia among homosexual men in the early 1980s that led to the identification of the (HIV ) human immunodeficiency virus and (AIDS) acquired immunodeficiency syndrome (AIDS); the outbreak in 2003 of a respiratory illness, later identified as severe acute respiratory syndrome (SARS), caused by a previously unrecognized virus; and periodic outbreaks of food poisoning caused by eating food contaminated with bacteria.

Cancer clusters may be suspected when people report that several family members, friends, neighbors, or coworkers have been diagnosed with the same or related cancer(s). In the 1960s, one of the best known cancer clusters emerged, involving many cases of mesothelioma (a rare cancer of the lining of the chest and abdomen).

Researchers traced the development of mesothelioma to exposure to asbestos, a fibrous mineral that was used heavily in shipbuilding during World War II and has also been used in manufacturing industrial and consumer products. Working with asbestos is the major risk factor (something that may increase the chance of developing a disease) for mesothelioma.

Facts About Cancer

Some concepts about cancer can be helpful when trying to understand suspected cancer clusters:

Cancer is the uncontrolled growth and spread of abnormal cells anywhere in the body. However, cancer is not just one disease; it is actually an umbrella term for at least 100 different but related diseases.

Each type of cancer has certain known and/or suspected risk factors associated with it.
Cancer is not caused by injuries, nor is it contagious. It cannot be passed from one person to another like a cold or flu virus.
Cancer is almost always caused by a combination of factors that interact in ways that are not yet fully understood.

Carcinogenesis (the process by which normal cells are transformed into cancer cells) involves a series of changes within cells that usually occur over many years. More than 10 years can go by between the exposure to a carcinogen (any substance that causes cancer) and a diagnosis of cancer, which makes it difficult to pinpoint the cause of that cancer.

Cancer is more likely to occur as people get older; because people are living longer, more cases of cancer can be expected in the future. This increased life expectancy may create the impression that cancer is becoming much more common, even though an increase in the number of cases of cancer is related in large part to the growing number of elderly people in the population.

Some racial and ethnic groups have higher rates of cancer than other racial and ethnic groups. Such differences 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, and other risk factors.

Cancer, in general, is common. More than 17 million new cases of cancer have been diagnosed since 1990.

Because most cancers are thought to be caused by a combination of factors related to genetics and environment (including behavior and lifestyle), studies of suspected cancer clusters usually focus on these two issues. Genetic factors are inherited, that is, passed from parents to children. However, establishing a genetic-environmental interaction (significant and valid evidence that a specific genetic factor leads to an increased chance that a particular environmental exposure will result in cancer) requires studies of large populations over long periods of time. Researchers are just beginning to learn about the roles genetics and environmental exposures play in carcinogenesis. Some of their discoveries are outlined below:

Genetics

All cancers develop because of genetic alterations of one kind or another. An alteration is a change or mutation in the physical structure of a gene that interferes with the gene’s normal functions.

Some genetic alterations that increase the risk of cancer are present at birth in the genes of all cells in the body, including reproductive cells. These changes, which are called germline mutations, can be passed from parent to child. This type of alteration is known as an inherited susceptibility; most cancers are not due to an inherited susceptibility.
Most cancers result from genetic changes that occur after birth during one’s lifetime. Genetic changes can occur in any cell that divides. These genetic changes are called somatic alterations.
Familial cancer clusters (cancer that occurs in families more often than would be expected by chance) have been reported for many types of cancer. Because cancer is a common disease, it is not unusual for several cases to occur within a family. Familial cancer clusters are sometimes linked to inherited susceptibility, but environmental factors and chance may also be involved.
Having an inherited susceptibility for a type of cancer does not necessarily mean that the individual will be diagnosed with the cancer; it means the chance of developing cancer increases if other factors that promote the development of cancer are present or are encountered later.

Environment

The term environment includes not only air, water, and soil, but also substances and conditions in the home and workplace. It also includes diet; the use of tobacco, alcohol, or drugs; exposure to chemicals; and exposure to sunlight and other forms of radiation.

People are exposed to a variety of environmental factors for varying lengths of time, and these factors interact in ways that are still not fully understood. Further, individuals have varying levels of susceptibility to these factors.
Hazardous substances are often found in higher levels in the workplace than in the general environment. For this reason, some workers may have greater and longer exposures to such substances than the general population. Findings of higher than expected numbers of cancer cases among workers in particular occupations or industries provide important leads regarding causes of cancer among the general public. In fact, occupational studies (studies of specific groups of workers) have identified many specific cancer-causing substances and have provided the motivation to find ways to reduce or eliminate exposures in the workplace and elsewhere.

Reporting Suspected Cancer Clusters

A suspected cancer cluster may be reported to a state or local health department or state cancer registry. State and local health departments and cancer registries use established criteria to investigate reports of cancer clusters. When a suspected cancer cluster is first reported, the investigating department or agency gathers information and gives the inquirer general information about cancer clusters.

Although investigators may use different processes, most follow a basic procedure in which increasingly specific information is obtained and analyzed in stages. Investigators are likely to request the following:

Information about the potential cluster: type(s) of cancer, number of cases, suspected exposure(s), and geographic area/time period of concern.

Information about each person with cancer in the potential cluster: name, address, telephone number, gender, race, age, occupation(s), as well as area(s) lived in/length of time.

Information about each case of cancer: type of cancer, date of diagnosis, age at diagnosis, possible causes, metastatic sites, and physician contact.

Most reports of suspected cancer clusters are resolved at this initial contact because concerned individuals realize that what seemed like a cancer cluster is not a true cluster. If further evaluation is needed, epidemiologists will take the following steps to investigate a possible cancer cluster:

Attempt to verify the reported cases by contacting patients and relatives and obtaining medical records.

Compare the number of cases in the suspected cancer cluster with information in census data and cancer registries to determine if there is a higher than expected number of cases.

Review the scientific literature to establish whether the reported cancer(s) has been linked to the suspected exposure.

Work with Federal agencies, if necessary, to gather additional information to help decide whether to conduct a comprehensive epidemiological study.

Subpages (1): Facts About Cancer Clusters

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