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Table of Contents What is screening?
General Information About Colorectal Cancer
Colorectal Cancer Screening
Risks of Colorectal Cancer Screening
Changes to This Summary (09/13/2004)
Questions or Comments About This Summary
To Learn More
About PDQ
What is screening?
Screening is looking for cancer before a person has any symptoms. This can help find
cancer at an early stage. When abnormal tissue or cancer is found early, it may
be easier to treat. By the time symptoms appear, cancer may have begun
to spread.
Scientists are trying to better understand which
people are more likely to get certain types of cancer. They also study the things
we do and the things around us to see if they cause cancer. This
information helps doctors recommend who should be screened for cancer, which
screening tests should be used, and how often the tests should be done.
It is important to remember that your doctor does not necessarily
think you have cancer if he or she suggests a screening test. Screening
tests are given when you have no cancer symptoms. Screening tests may be repeated on a regular basis.
If a screening test result is abnormal, you may need to have more tests done to find out if you have cancer. These are called diagnostic tests. Refer to the following PDQ summaries for information about prevention, diagnosis, and treatment of colorectal cancer:
 Back to Top General Information About Colorectal Cancer
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Colorectal cancer is a disease in which malignant (cancer)
cells form in the tissues of the colon or the rectum.
The colon and rectum are parts of the body's digestive system. The digestive system removes and
processes nutrients (vitamins, minerals, carbohydrates, fats, proteins, and
water) from foods and helps pass waste material out of the body. The digestive
system is made up of the mouth, throat, esophagus,
stomach, and the
small and large
intestines. The first 6 feet of the
large intestine are called the large bowel or colon. The last 6 inches are the
rectum and the anal canal. The anal
canal ends at the anus (the opening
of the large intestine to the outside of the body).
Cancer that begins in the colon is called colon cancer, and cancer
that begins in the rectum is called rectal cancer. Cancer that begins in either of
these organs may also be called colorectal cancer.
Colorectal cancer is the second leading cause of death from
cancer in the United States.
In recent years (1995-1999), the number of people diagnosed with colorectal cancer has stayed about the same, but the number of people who die from colorectal cancer has decreased. Colorectal cancer is found more often in men than
in women.
Age and health history can affect the risk of developing colon cancer.
Anything that increases a person's chance of getting a disease
is called a risk factor. Risk factors for colorectal cancer include the
following:
Refer to the PDQ summary on Genetics of Colorectal Cancer for more information about family history and colorectal cancer screening.
Back to Top Colorectal Cancer Screening
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Tests are used to screen for different types of cancer.
Some screening tests are used because they have been shown to be helpful both in finding cancers early and decreasing the chance of dying from these cancers. Other tests are used because they have been shown to find cancer in some people; however, it has not been proven in clinical trials that use of these tests will decrease the risk of dying from cancer. Scientists study screening tests to find those with the fewest risks and most benefits. Cancer screening trials also are meant to show whether early detection (finding cancer before it causes symptoms) decreases a person's chance of dying from the disease. For some types of cancer, finding and treating the disease at an early stage may result in a better chance of recovery. Clinical trials that study cancer screening methods are taking place in many parts of the country. Information about ongoing clinical trials is available from the NCI Cancer.gov Web site.
Five tests are commonly used to screen for colorectal
cancer:
Fecal occult blood test
A fecal occult blood test (FOBT) checks stool (solid waste) for blood that can only be seen with a microscope. Small samples of stool are placed on special cards and returned to the doctor or laboratory for testing. Blood in the stool may be a sign of polyps or cancer.
Sigmoidoscopy
Sigmoidoscopy is a procedure to look inside the rectum and sigmoid (lower) colon for polyps, abnormal areas, or cancer. A sigmoidoscope (a thin, lighted tube) is inserted through the rectum into the sigmoid colon. Polyps or tissue samples may be taken for biopsy. A sigmoidoscopy and a digital rectal exam (DRE) may be used together to screen for colorectal cancer.
Barium enema
A barium enema (BE) is a series of x-rays of the lower gastrointestinal tract. A liquid that contains barium (a silver-white metallic compound) is put into the rectum. The barium coats the lower gastrointestinal tract and x-rays are taken. This procedure is also called a lower GI series.
Colonoscopy
Colonoscopy is a procedure to look inside the rectum and colon for polyps, abnormal areas, or cancer. A colonoscope (a thin, lighted tube) is inserted through the rectum into the colon. Polyps or tissue samples may be taken for biopsy.
Digital rectal exam
A digital rectal exam (DRE) is an exam of the rectum. The doctor or nurse inserts a lubricated, gloved finger into the lower part of the rectum to feel for lumps or anything else that seems unusual.
Other screening tests are being studied in clinical
trials.
Virtual colonoscopy
Virtual colonoscopy is a procedure that uses a series of x-rays called computed tomography to make a series of pictures of the
colon. A computer puts the pictures together to create detailed images that may
show polyps and anything else that seems unusual on the inside surface of the colon. This test is also called colonography or CT colonography. Clinical trials are comparing
virtual colonoscopy with commonly used colorectal cancer screening tests.
DNA stool test
This test checks DNA in stool cells for genetic changes that may be a sign of colorectal cancer.
Screening clinical trials are taking place in many parts of the country.
Information about ongoing clinical trials is available from the
NCI Cancer.gov Web
site.
Back to Top Risks of Colorectal Cancer Screening
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Screening tests have risks.
Decisions about screening tests can be difficult. Not all screening tests are helpful and most have risks. Before having any screening test, you may
want to discuss the test with your doctor. It is important to know the risks of
the test and whether it has been proven to reduce the risk of dying from
cancer.
The risks of colorectal cancer screening tests include the following:
Damage to the colon can occur.
Infection or tears in the lining of the colon can result from
sigmoidoscopy, colonoscopy, or the removal of polyps found by screening.
False-negative test results can occur.
Screening test results may appear to be normal even though colorectal
cancer is present. A person who receives a false-negative test result (one that
shows there is no cancer when there really is) may delay seeking medical
care for symptoms.
False-positive test results can occur.
Screening test results may appear to be abnormal even though no
cancer is present. A false-positive test result (one that shows there is cancer when there really isn't) can cause anxiety and is usually followed by more tests (such as
biopsy), which also have risks.
Your doctor can advise you about your risk for colorectal cancer and your need for screening tests.
Back to Top Changes to This Summary (09/13/2004)
The PDQ cancer information summaries are reviewed regularly and updated as new information becomes available. This section describes the latest changes made to this summary as of the date above.
Editorial changes were made to this summary.
Back to Top Questions or Comments About This Summary
If you have questions or comments about this summary, please send them to Cancer.gov through the Web site’s Contact Form. We can respond only to email messages written in English.
Back to Top To Learn More
Call For more information, U.S. residents may call the National Cancer Institute's (NCI's) Cancer Information Service toll-free at 1-800-4-CANCER (1-800-422-6237) Monday through Friday from 9:00 a.m. to 4:30 p.m. Deaf and hard-of-hearing callers with TTY equipment may call 1-800-332-8615. The call is free and a trained Cancer Information Specialist is available to answer your questions. Web sites and Organizations The NCI's Cancer.gov Web site provides online access to information on cancer, clinical trials, and other Web sites and organizations that offer support and resources for cancer patients and their families. There are also many other places where people can get materials and information about cancer treatment and services. Local hospitals may have information on local and regional agencies that offer information about finances, getting to and from treatment, receiving care at home, and dealing with problems associated with cancer treatment. Publications The NCI has booklets and other materials for patients, health professionals, and the public. These publications discuss types of cancer, methods of cancer treatment, coping with cancer, and clinical trials. Some publications provide information on tests for cancer, cancer causes and prevention, cancer statistics, and NCI research activities. NCI materials on these and other topics may be ordered online or printed directly from the NCI Publications Locator. These materials can also be ordered by telephone from the Cancer Information Service toll-free at 1-800-4-CANCER (1-800-422-6237), TTY at 1-800-332-8615. LiveHelp The NCI's LiveHelp service, a program available on several of the Institute's Web sites, provides Internet users with the ability to chat online with an Information Specialist. The service is available from 9:00 a.m. to 10:00 p.m. Eastern time, Monday through Friday. Information Specialists can help Internet users find information on NCI Web sites and answer questions about cancer. Write For more information from the NCI, please write to this address: - NCI Public Inquiries Office
- Suite 3036A
- 6116 Executive Boulevard, MSC8322
- Bethesda, MD 20892-8322
Back to Top About PDQ
PDQ is a comprehensive cancer database available on Cancer.gov. PDQ is the National Cancer Institute's (NCI's) comprehensive cancer information database. Most of the information contained in PDQ is available online at Cancer.gov, the NCI's Web site. PDQ is provided as a service of the NCI. The NCI is part of the National Institutes of Health, the federal government's focal point for biomedical research. PDQ contains cancer information summaries. The PDQ database contains summaries of the latest published information on cancer prevention, detection, genetics, treatment, supportive care, and complementary and alternative medicine. Most summaries are available in two versions. The health professional versions provide detailed information written in technical language. The patient versions are written in easy-to-understand, nontechnical language. Both versions provide current and accurate cancer information. The PDQ cancer information summaries are developed by cancer experts and reviewed regularly. Editorial Boards made up of experts in oncology and related specialties are responsible for writing and maintaining the cancer information summaries. The summaries are reviewed regularly and changes are made as new information becomes available. The date on each summary ("Date Last Modified") indicates the time of the most recent change. PDQ also contains information on clinical trials. People who are at high risk for a certain type of cancer may want to take part in a clinical trial. A clinical trial is a study to answer a scientific question, such as whether a method of finding cancer earlier can help people to live longer. Trials are based on past studies and what has been learned in the laboratory. Each trial answers certain scientific questions in order to find new and better ways to help cancer patients and those who are at risk for cancer. During screening clinical trials, information is collected about screening methods, the risks involved, and how well they do or do not work. If a clinical trial shows that a new method is better than one currently being used, the new method may become "standard." Listings of clinical trials are included in PDQ and are available online at Cancer.gov. Descriptions of the trials are available in health professional and patient versions. Many cancer doctors who take part in clinical trials are also listed in PDQ. For more information, call the Cancer Information Service 1-800-4-CANCER (1-800-422-6237); TTY at 1-800-332-8615.
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