Cancer and the Environment : Part 5

by National Cancer Institute

(Page 5 of 5)

Human Studies

Human studies are the way to decide with the most certainty whether a substance causes cancer.

By following groups of people over time, researchers may be able to see whether certain exposures lead to cancer. They also compare a group of people who have been diagnosed with a type of cancer to another group of people without the disease. Sometimes the group with cancer has patterns of exposures very different from the patterns in the group without cancer.

Many environmental causes of cancer have first been noticed in the workplace, because people in certain occupations have higher exposures to some chemicals than do people in the general population.

Animal Studies

Rodents (mice and rats) are commonly used in studies of environmental causes of cancer. They have a relatively short lifespan (2 to 3 years), and their bodies' responses to known cancer causing chemicals are similar to a human response. Dietary studies in rodents are more difficult, however, due to differences in the digestive systems of rodents and humans.

In animal studies, the chemical exposures are usually at much higher levels than would be seen with human exposure. If an extremely high level of exposure does not lead to cancer, researchers reason that the chemical most likely does not cause cancer at lower levels either.

Laboratory Studies of Human Cells

Researchers study human cells in the laboratory to see whether certain chemicals might cause changes that could lead to cancer.

These studies are often done to see if animal studies--which take longer and are more complex-- are actually needed. If a chemical does not cause cancer in laboratory cells, animal studies usually aren't done.

Risk Assessment

How do scientists decide which exposures are high risk and which are low risk? Risk assessment involves three factors:

1. Potency: The potential of a given amount of a substance to cause cancer. Benzene, for example, is quite potent because even small amounts of it can increase cancer risk. Other compounds, such as chloroform, are less potent; they require higher exposures to increase the risk by the same degree.

2. Type of exposure: Whether the exposure is one-time (acute) or long-term (chronic), and whether it is unavoidable (in the workplace, for example, or in the air we breathe).

3. Dose response: A dose-response trend describes what happens to cancer risk as the level of exposure increases or decreases.

Occupational Cancer Risks

Certain occupations carry an increased cancer risk: these include painters; furniture makers; workers in the iron, steel, coal, and rubber industries; and workers involved in shoe manufacturing and repair.

Always use proper protective equipment when handling chemicals, and clean spills immediately.

Ask at your workplace about Material Safety Data Sheets, which contain information about hazardous substances.

Cancer Screening for Early Detection

Cancer screening tests help detect cancer at an early stage, which allows treatment to occur before the cancer spreads.

Get screened regularly for these cancers:

Colon/rectum: Tests include the fecal occult blood test, sigmoidoscopy, and colonoscopy.

Breast: The standard screening test is a mammogram, or X-ray of the breast tissue.

Cervix: The standard screening test is the Pap smear.

Guidelines for when testing should begin and how often it should occur may be different for each person, so talk with your doctor about what's right for you.

Also talk with your health care provider about exposures at work and at home, and discuss whether your family or personal history may put you at risk for certain types of cancer. Your doctor may recommend other cancer screening tests as well.

Always Remember the Avoidable Risks

While it is always prudent to be aware of environmental exposures to carcinogens, one must also remember that the major environmental factors linked to cancer deaths can be avoided, because most of them involve behavior choices. More than half of all cancer deaths could be prevented by eliminating the use of tobacco products, moderating the use of alcohol, and making better dietary choices.

About the Author

www.nci.nih.gov
The National Cancer Institute's research programs are extensive and contain many innovative initiatives. I invite you to explore our Web site to find out more about the exciting work being conducted here at NCI and by NCI-supported scientists throughout the country.