The following table outlines some of the advantages and disadvantages of the colorectal cancer screening tests described in this fact sheet.

Table: Advantages and Disadvantages of Colorectal Cancer Screening Tests

Fecal Occult Blood Test (FOBT)
Advantages
* No preparation of the colon is necessary.
* Samples can be collected at home.
* Cost is low compared to other colorectal screening tests.
* There is no risk of infection or tears in the lining of the colon.
Disadvantages 
* This test fails to detect most polyps and some cancers.
* False positive results are possible. (“False positive” means the test suggests an abnormality when none is present.)
* Dietary and other limitations, such as increasing fiber intake and avoiding meat, certain vegetables, vitamin C, iron, and aspirin, are necessary for several days before the test.
* Additional procedures, such as colonoscopy, may be necessary if the test indicates an abnormality.

Sigmoidoscopy
Advantages 
* The test is usually quick, with few complications.
* Discomfort is minimal.
* The doctor can perform a biopsy (the removal of tissue for examination under a microscope by a pathologist) and remove polyps during the test, if necessary.
* Less extensive preparation of the colon is necessary with this test than for a colonoscopy.
Disadvantages 
* This test allows the doctor to view only the rectum and the lower part of the colon. Any polyps in the upper part of the colon will be missed.
* There is a very small risk of infection or tears in the lining of the colon.
* Additional procedures, such as colonoscopy, may be necessary if the test indicates an abnormality.

Colonoscopy
Advantages 
* This test allows the doctor to view the rectum and the entire colon.
* The doctor can perform a biopsy and remove polyps during the test, if necessary.
Disadvantages 
* The test may not detect some small polyps and cancers.
* Thorough preparation of the colon is necessary before the test.
* Sedation is usually needed.
* Complications, such as infection and/or tears in the lining of the colon, can occur.

Double Contrast Barium Enema (DCBE)
Advantages 
* This test usually allows the doctor to view the rectum and the entire colon.
* Complications are rare.
* No sedation is necessary.
* Discomfort is minimal.
Disadvantages 
* The test may not detect some small polyps and cancers.
* Thorough preparation of the colon is necessary before the test.
* False positive results are possible.
* The doctor cannot perform a biopsy or remove polyps during the test.
* Additional procedures are necessary if the test indicates an abnormality.

6.  Do insurance companies pay for colorectal cancer screening?

Insurance coverage varies. People should check with their health insurance provider to determine their colorectal cancer screening benefits. Medicare covers several colorectal cancer screening tests for its beneficiaries. Specific information about Medicare benefits is available on the Medicare Web site at http://www.medicare.gov/health/overview.asp on the Internet.

7.  What happens if a colorectal cancer screening test shows an abnormality?

If screening tests find an abnormality, the health care provider will perform a physical exam and evaluate the person’s personal and family medical history. Additional diagnostic tests may be ordered. These may include x-rays of the gastrointestinal tract, sigmoidoscopy, or colonoscopy (see question 4). The health care provider may also order a blood test called a CEA assay to measure carcinoembryonic antigen, a protein that is sometimes present in higher levels in patients with colorectal cancer.

If an abnormal area is found during a sigmoidoscopy or colonoscopy, a biopsy is performed to determine if cancer is present.

The NCI booklet What You Need To Know About™ Cancer of the Colon and Rectum provides more information about the diagnosis and treatment of colorectal cancer. This publication and other cancer resources are available from the NCI Publications Locator at http://cancer.gov/publications on the Internet, or by calling the Cancer Information Service (CIS) toll-free at 1–800–4–CANCER (1–800–422–6237) (see below). Additional information about colorectal cancer is available on the NCI’s Web site at http://cancer.gov/colon on the Internet.

8. Are new tests under study for colorectal cancer screening?

Several new tests for colorectal cancer screening and diagnosis are under study. For example, virtual colonoscopy (also called computed tomographic colonography) is a procedure that uses special x-ray equipment to produce pictures of the colon. A computer then assembles these pictures into detailed images that can show polyps and other abnormalities. Because it is less invasive and does not require sedation, virtual colonoscopy may cause less discomfort and take less time than conventional colonoscopy. However, unlike conventional colonoscopy, it is not possible to remove polyps or perform a biopsy during this test. An additional procedure, such as conventional colonoscopy, is needed if the virtual procedure finds a potential problem. Clinical trials (research studies with people) are under way to compare the advantages and disadvantages of virtual colonoscopy with those of other colorectal cancer screening tests.

Genetic testing of stool samples is also under study as a possible way to screen for colorectal cancer. The lining of the colon is constantly shedding cells into the stool. Testing stool samples for genetic alterations that occur in colorectal cancer cells may help doctors find evidence of cancer. Research conducted thus far has shown that this test can detect colorectal cancer in people already diagnosed with this disease by other means. However, more studies are needed to determine whether the test can detect colorectal cancer in people who do not have symptoms.

Additional information about clinical trials to test new methods for colorectal cancer screening is available from the NCI’s Web site at http://cancer.gov/clinical_trials/ on the Internet, or by calling the CIS at 1–800–4–CANCER (1–800–422–6237).

References

Dong SM, Traverso G, Johnson C, et al. Detecting colorectal cancer in stool with the use of multiple genetic targets. Journal of the National Cancer Institute 2001; 93(11):858–865.

Fenlon HM, Nunes DP, Schroy III PC, et al. A comparison of virtual and conventional colonoscopy for the detection of colorectal polyps. The New England Journal of Medicine 1999; 341(20):1496–1503.

Levin B. Overview of colorectal cancer screening in the United States. Journal of Psychological Oncology 2001; 19(3/4):9–19.

Lieberman DA, Harford WV, Ahnen DJ, et al. One-time screening for colorectal cancer with combined fecal occult-blood testing and examination of the distal colon. New England Journal of Medicine 2001; 345(8):555–560.

Lieberman DA, Weiss DG, Bond JH, et al. Use of colonoscopy to screen asymptomatic adults for colorectal cancer. New England Journal of Medicine 2000; 343(3):162–168.

Mandel JS, Church TR, Ederer F, Bond JH. Colorectal cancer mortality: Effectiveness of biennial screening for fecal occult blood. Journal of the National Cancer Institute 1999; 91(5):434–437.

Ransohoff DF, Sandler RS. Screening for colorectal cancer. New England Journal of Medicine 2002; 346(1):40–44.

Winawer SJ, Stewart ET, Zauber AG, et al. A comparison of colonoscopy and double-contrast barium enema for surveillance after polypectomy. New England Journal of Medicine 2000; 342(24):1766–1772.

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For more information on colorectal cancer, please visit the  Colorectal Cancer Home Page.

 Published and reviewed by NCI on 04/03/2002