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Colorectal Cancer Screening: Questions and Answers

1. What is colorectal cancer?

Colorectal cancer is a disease in which cells in the colon or rectum become abnormal and 

divide without normal control or order, forming a mass called a tumor. (The colon and 

rectum are parts of the body’s digestive system that remove water and nutrients from 

food and store solid waste until it passes out of the body.) Cancer cells invade and 

destroy the tissue around them. They can also break away from the tumor and spread to 

form new tumors in other parts of the body. 

Colorectal cancer is the third most common type of non-skin cancer in men (after prostate 

cancer and lung cancer) and in women (after breast cancer and lung cancer). It is the 

second leading cause of cancer death in the United States after lung cancer. The rate of 

Key Points 

• Colorectal cancer is a disease in which cells in the colon or rectum 

become abnormal and divide without normal control or order, forming a 

mass called a tumor (see Question 1). 

• The exact causes of colorectal cancer are not known. However, studies 

show that certain factors increase a person’s chance of developing 

colorectal cancer (see Question 2). 

• Health care providers may suggest one or more tests for colorectal cancer 

screening, including fecal occult blood test (FOBT), sigmoidoscopy, 

colonoscopy, double contrast barium enema (DCBE), or digital rectal 

exam (DRE) (see Question 4). 

• People should talk with their health care providers about when to begin 

screening for colorectal cancer, what tests to have, the benefits and risks 

of each test, and how often to schedule appointments (see Question 5). 

• New ways to screen for colorectal cancer are under study (see 

Question 8). 
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new cases and deaths resulting from this disease is decreasing. Still, over 147,000 new 

cases are diagnosed, and more than 57,000 people die from colorectal cancer each year. 

2. Who is at risk for colorectal cancer?

The exact causes of colorectal cancer are not known. However, studies show that certain 

factors are linked to an increased chance of developing colorectal cancer: 

• Age⎯Colorectal cancer is more likely to occur as people get older. Although the 

disease can occur at any age, most people who develop colorectal cancer are over the 

age of 50. 

• Polyps⎯Polyps are growths that protrude from the inner wall of the colon or rectum. 

They are relatively common in people over age 50. Most polyps are benign 

(noncancerous); however, experts believe that most colorectal cancers develop in 

certain polyps, called adenomas. Therefore, detecting and removing these growths 

may help prevent colorectal cancer. The procedure to remove polyps is called a 

polypectomy. 

Familial adenomatous polyposis, or FAP, is a rare, inherited condition in which 

hundreds of polyps develop in the colon and rectum. Because this condition is 

extremely likely to lead to colorectal cancer, it is often treated with surgery to 

remove the colon and rectum (colectomy). Rectum-sparing surgery may be an 

option. Also, the FDA has approved an anti-inflammatory drug, celecoxib, for the 

treatment of FAP. Doctors may prescribe this drug, in addition to surveillance 

and surgery, to manage FAP. 

• Personal history⎯A person who has already had colorectal cancer is at an increased 

risk of developing colorectal cancer a second time. Also, research studies show that 

some women with a history of ovarian, uterine, or breast cancer have a 

higher-than-average chance of developing colorectal cancer. 

• Family history⎯Close relatives (parents, siblings, or children) of a person who has 

had colorectal cancer are somewhat more likely to develop this type of cancer 

themselves, especially if the family member developed the cancer at a young age. If 

many family members have had colorectal cancer, the chances increase even more. 

• Ulcerative colitis or Crohn’s colitis⎯Ulcerative colitis is a condition that causes 

inflammation and sores (ulcers) in the lining of the colon. Crohn’s colitis (also 

called Crohn’s disease) causes chronic inflammation of the gastrointestinal tract, 

most often the small intestine (the part of the digestive tract that is located 

between the stomach and the large intestine). People who have ulcerative colitis 

or Crohn’s colitis may be more likely to develop colorectal cancer than people 

who do not have these conditions. 
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• Diet⎯Some evidence suggests that the development of colorectal cancer may be 

associated with a diet that is high in fat and calories and low in foods with fiber, such 

as whole grains, fruits, and vegetables. Researchers are exploring what role these and 

other dietary components play in the development of colorectal cancer.

• Exercise⎯Some evidence suggests that a sedentary lifestyle may be associated with 

an increased risk of colorectal cancer. In contrast, people who exercise regularly may 

have a decreased risk of developing colorectal cancer.

3. What is screening, and why is it important?

Screening means checking for health problems before they cause symptoms. Screening 

can find polyps that may eventually become cancerous (precancerous polyps), as well as 

some cancers in an early stage, before they spread to other parts of the body. 

Colorectal cancer screening is used to detect cancer, precancerous polyps, or other 

abnormal conditions. If screening detects an abnormality, diagnosis and treatment can 

occur promptly. In addition, finding and treating polyps may be one of the most effective 

ways to prevent the development of cancer altogether. Colorectal cancer is generally 

more treatable when it is found early. 

4. What methods are used to screen people for colorectal cancer?

Health care providers may suggest one or more of the tests listed below for colorectal 

cancer screening. 

• A fecal occult blood test (FOBT) checks for hidden blood in the stool. Studies have 

proven that this test, when performed every 1 to 2 years in people ages 50 to 80, 

reduces the number of deaths due to colorectal cancer by as much as 30 percent. 

• A sigmoidoscopy is an examination of the rectum and lower colon using a lighted 

instrument called a sigmoidoscope. Sigmoidoscopy can find precancerous or 

cancerous growths in the rectum and lower colon. Studies suggest that regular 

screening with sigmoidoscopy after age 50 can reduce the number of deaths from 

colorectal cancer. 

 

• A colonoscopy is an examination of the rectum and entire colon using a lighted 

instrument called a colonoscope. Colonoscopy can find precancerous or cancerous 

growths throughout the colon, including the upper part of the colon, where they 

would be missed by sigmoidoscopy. However, it is not known whether this benefit 

outweighs the risks of colonoscopy, which include bleeding and puncturing of the 

lining of the colon. More research is needed to address these issues. 
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• A double contrast barium enema (DCBE) is a series of x-rays of the entire colon 

and rectum. The x-rays are taken after the patient is given an enema with a barium 

solution and air is introduced into the colon. The barium and air help to outline the 

colon and rectum on the x-rays. Research shows that DCBE may miss small polyps. 

• A digital rectal exam (DRE) is often part of a routine physical examination. The 

health care provider inserts a lubricated, gloved finger into the rectum to feel for 

abnormal areas. DRE allows for examination of only the lower part of the rectum. 

Scientists are still studying colorectal cancer screening methods, both alone and in 

combination, to determine how effective they are. Studies are also under way to clarify 

the risks of each test. 

See Question 5 for a table outlining some of the advantages and disadvantages of 

colorectal cancer screening tests. Additional information about these tests is available 

from the National Cancer Institute’s (NCI) Web site at http:// www.cancer.gov/colon on 

the Internet. 

5. How can people and their health care providers decide which colorectal cancer 

screening test(s) to use and how often to be screened? 

Several major organizations, including the U.S. Preventive Services Task Force (a group 

of experts convened by the U.S. Public Health Service), the American Cancer Society, 

and professional societies, have developed guidelines for colorectal cancer screening. 

Although some details of their recommendations vary regarding which screening tests to 

use and how often to be screened, all of these organizations support screening for 

colorectal cancer. 

People should talk with their health care provider about when to begin screening for 

colorectal cancer, what tests to have, the benefits and risks of each test, and how often to 

schedule appointments. 

The decision to have a certain test will take into account several factors: 

• Person’s age, medical history, family history, and general health; 

• Accuracy of the test; 

• Risks associated with the test; 

• Preparation required before the test; 

• Sedation necessary during the test; 

• Follow-up care after the test; 

• Convenience of the test; and 

• Cost and insurance coverage of the test. 
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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 

Test Advantages Disadvantages 

Fecal Occult 

Blood Test 

(FOBT) 

• No preparation of the colon 

is necessary. 

• Samples can be collected at 

home. 

• Cost is low compared to 

other colorectal cancer 

screening tests. 

• FOBT does not cause 

bleeding or tears in the 

lining of the colon. 

• 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 often recommended 

for several days before the test. 

• Additional procedures, such as 

colonoscopy, may be necessary 

if the test indicates an 

abnormality. 

Sigmoidoscopy • The test is usually quick, 

with few complications. 

• Discomfort is minimal. 

• In some cases, the doctor 

may be able to 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. 

• 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 

bleeding or tears in the lining of 

the colon. 

• Additional procedures, such as 

colonoscopy, may be necessary 

if the test indicates an 

abnormality. 
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Test Advantages Disadvantages 

Colonoscopy • 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. 

• The test may not detect all small 

polyps and cancers, but it is the 

most sensitive test currently 

available. 

• Thorough preparation of the 

colon is necessary before the 

test. 

• Sedation is usually needed. 

• Although uncommon, 

complications such as bleeding 

and/or tears in the lining of the 

colon can occur. 

Double 

Contrast 

Barium Enema 

(DCBE) 

• This test usually allows the 

doctor to view the rectum 

and the entire colon. 

• Complications are rare. 

• No sedation is necessary. 

• 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. 

Digital Rectal 

Exam (DRE) 

• Often part of a routine 

physical examination. 

• No preparation of the colon 

is necessary. 

• The test is usually quick and 

painless. 

• The test can detect 

abnormalities only in the lower 

part of the rectum. 

• 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 
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diagnostic tests may be ordered. These may include x-rays of the gastrointestinal tract, 

sigmoidoscopy, or most often, 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 colonoscopy, a biopsy is performed to determine if 

cancer is present. If an abnormal area is found during a sigmoidoscopy, a biopsy may be 

performed during the test, and a colonoscopy may be recommended. 

More information about colorectal cancer screening tests is available in Colorectal 

Cancer (PDQ®): Screening. This summary of information from PDQ, the NCI’s 

comprehensive cancer information database, can be found at 

http://www.cancer.gov/cancerinfo/pdq/screening/colorectal/patient/ on the Internet. 

The NCI booklet What You Need To Know AboutTM Cancer of the Colon and Rectum

provides more information about the diagnosis and treatment of colorectal cancer. This 

publication and other resources are available from the NCI Publications Locator at 

http://www.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://www.cancer.gov/cancerinfo/types/colon-and-rectal/ or 

http://www.cancer.gov/colon on the Internet. 

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

New tests for colorectal cancer screening 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, as with 

conventional colonoscopy and DCBE, thorough preparation of the colon is necessary 

before the test. 

Unlike conventional colonoscopy, it is not possible to remove polyps or perform a biopsy 

during virtual colonoscopy. 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 or precancerous polyps. 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 
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can detect colorectal cancer or precancerous polyps 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://www.cancer.gov/clinicaltrials/ on 

the Internet, or by calling the CIS at 1−800−4−CANCER (1−800−422−6237). 

Selected References 

Anderson WF, Guyton KZ, Hiatt RA, et al. Colorectal cancer screening for persons at average 

risk. Journal of the National Cancer Institute 2002; 94(15):1126−1133. 

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. 

Gatto NM, Frucht H, Sundararajan V, et al. Risk of perforation after colonoscopy and 

sigmoidoscopy: A population-based study. Journal of the National Cancer Institute 2003; 

95(3):230−236. 

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, Bond JH, et al. The effect of fecal occult-blood screening on the 

incidence of colorectal cancer. New England Journal of Medicine 2000; 343(22):1603−1607. 

Pickhardt PJ, Choi JR, Hwang I, et al. Computed tomographic virtual colonoscopy to screen for 

colorectal neoplasia in asymptomatic adults. New England Journal of Medicine 2003; 

349(23):2191–2200. 

Ransohoff DF, Sandler RS. Screening for colorectal cancer. New England Journal of Medicine

2002; 346(1):40−44. 

Walsh JME, Terdiman JP. Colorectal cancer screening: Scientific review. Journal of the 

American Medical Association 2003; 289(10):1288−1296. 
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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. 

Yee J, Akerkar GA, Hung RK, et al. Colorectal neoplasia: Performance characteristics of CT 

colonography for detection in 300 patients. Radiology 2001; 219(3):685−692. 

# # # 

Related Resources

Publications (available at http://www.cancer.gov/publications) 

• Men Eat 9 A Day 

• Time To Take Five: Eat 5 Fruits and Vegetables Every Day 

• What You Need To Know AboutTM Cancer of the Colon and Rectum 

National Cancer Institute (NCI) Resources

Cancer Information Service (toll-free)

 Telephone: 1–800–4–CANCER (1–800–422–6237) 

 TTY: 1–800–332–8615 

Online 

NCI’s Web site: http://www.cancer.gov 

LiveHelp, NCI’s live online assistance: 

https://cissecure.nci.nih.gov/livehelp/welcome.asp

This fact sheet was reviewed on 6/9/04