Please note: This information was current at the time of publication but now may be out of date. This handout provides a general overview and may not apply to everyone. 

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Am Fam Physician. 2000;61(6):1773-1774

See related article on colorectal cancer.

What is colorectal cancer?

Colorectal cancer is cancer of the colon or rectum. The colon is the large intestine, and the rectum is the part of the large intestine that is closest to the anus (the outside opening to the intestine).

Colorectal cancer is a leading cause of cancer deaths in the United States. It caused about 56,500 deaths in 1999. Many of these deaths happened because the cancers were found too late to be cured. If colorectal cancer is found early enough, it can usually be cured by surgery.

What are the signs of colorectal cancer?

Most colorectal cancers begin as a polyp, a small, harmless growth in the wall of the colon (say “polyp” this way: pahl-ip). As the polyp grows, it can keep your intestine from working properly.

See your doctor if you have any of these warning signs:

  • Bleeding from your rectum

  • Blood in your stool or in the toilet after you have a bowel movement

  • A change in the shape of your stool

  • Cramping pain in your lower stomach

  • A feeling of discomfort or an urge to have a bowel movement when there is no need to have one

Other conditions can cause these same symptoms. You should be checked by your doctor to find the reason for your symptoms.

What are screening tests for colorectal cancer?

Screening tests are used to find cancers before they are large enough to cause any warning signs. Because finding cancer early means that you're more likely to be cured, it is important for you to have screening tests. Your doctor will choose the tests that are best for you.

Digital Rectal Exam. In this exam, your doctor uses a gloved finger to find any growths in your rectum. Because this exam can find less than 10 percent of colorectal cancers, it must be used along with another screening test.

Fecal Occult Blood Test. In this test, your stool is checked for blood that you can't see. If blood is found, another test is done to look for a polyp, a cancer or another cause of bleeding.

Many things that you eat can make this test turn out positive even though you don't really have blood in your stool (this is called a “false-positive” test). These things include some raw vegetables, horseradish, rare red meat, iron supplements and aspirin. Don't eat these things for two days before you have a fecal occult blood test.

Flexible Sigmoidoscopy. In this test, your doctor puts a thin, flexible tube with a light on the end into your rectum. Then the doctor looks at the lower part of your colon.

This test can be a bit uncomfortable, but it lets your doctor see polyps when they are very small (before they can be found with a fecal occult blood test).

Double-Contrast Barium Enema. For this test, you are given an enema with a liquid that makes your colon show up on an x-ray. Your doctor looks at the x-ray to find abnormal spots in your entire colon. If you have an abnormal spot, you are then examined by colonoscopy.

Colonoscopy. Before you have this test, you are given a medicine to make you sleepy. A thin, flexible tube is put into your rectum, and the doctor looks at your whole colon. The tube can also be used to remove polyps and cancers during the exam.

When should I be screened for colorectal cancer?

Colorectal cancer is more common in older people, so doctors usually screen patients after the age of 50 years. Some people have risk factors that make them more likely to get colorectal cancer at a young age. Screening should begin earlier in these people.

You should begin screening at a younger age if you have:

  • Had colorectal cancer or large polyps in the past

  • A close relative (brother, sister, parent or child) who had colorectal cancer

  • Ulcerative colitis or Crohn's disease

  • A hereditary colon cancer syndrome

If you are in one of these groups, you may also need to be tested more often than a person who doesn't have risk factors for colorectal cancer.

The U.S. Agency for Healthcare Research and Quality recommends any one of the following screening programs, beginning at the age of 50 years:

  • Fecal occult blood testing every year

  • Flexible sigmoidoscopy every 5 years

  • Fecal occult blood testing every year and flexible sigmoidoscopy every 5 years

  • Double-contrast barium enema every 5 to 10 years

  • Colonoscopy every 10 years

The American Academy of Family Physicians believes that any of these tests or combinations of tests is a good screening method. The American Cancer Society has similar guidelines.

Talk to your family doctor to decide which screening tests you should have and how often you should be screened. If you don't have any risk factors for colorectal cancer, you will probably have your first screening test around 50 years of age.

For more information on colorectal cancer screening, visit the American Cancer Society's Web site at

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