Colorectal cancer happens when cells that are not normal grow in your colon or rectum . Most people just call it "colon cancer."

These cancers usually begin as polyps, which are growths attached to the inside of the colon or rectum. Colon polyps are common, and most of them do not turn into cancer. Polyps are found during some screening tests. And polyps found during a colonoscopy or sigmoidoscopy usually can be removed at the same time.

When colon cancer is found early through screening tests, it is more easily treated.

Screening tests can detect or prevent this cancer, but only about half of people older than 50 are screened. According to the American Cancer Society, if everyone were tested, tens of thousands of lives could be saved each year.

A family history of colon cancer makes you more likely to get it. You will need to be screened at an earlier age—and have more frequent screening—than other people if:

• You have a close relative with colon cancer. You are more likely to get colon cancer if:
  • One of your parents, brothers, sisters, or children had it before the age of 60.
  • Two or more of your parents, brothers, sisters, or children has had it at any age.
• You have a family history of certain colon problems, such as familial adenomatous polyposis (FAP) or hereditary nonpolyposis colon cancer (HNPCC). Most people who inherit these conditions will get colon cancer if they are not screened and treated.

Stool tests involve sending some of your stool to a lab for testing to see if there is evidence of cancer. They don't help prevent colon cancer, but they do help find it early, when it is more treatable.

Stool tests need to be done once a year to find colon cancer as early as possible. These tests can usually be done in the privacy of your home.

There are three types of stool tests:

• Fecal occult blood test (FOBT). This is the most common stool test. You put tiny samples of your stool on a special card or cloth and send it to a lab. The lab uses certain chemicals to find blood that you can't see with the naked eye. FOBT tests don't cost much.
• Fecal immunochemical test (FIT). This is a newer test that is a little easier to do at home. It costs more than an FOBT.
• Stool DNA test (sDNA). This is the newest stool test. It looks for changes in DNA (genetic material) in the stool. It costs the most.

If you can't or won't go to the doctor to get an at-home stool test, you can check your local drugstore for an over-the-counter brand. But you may feel better if you talk to your doctor about what the test results mean.

Risks of stool tests

There is no risk involved in the actual use of a stool test. But there are some things you need to think about:

• Blood in the stool can be a sign of colon cancer, but it's more often caused by something else, such as hemorrhoids, ulcers, or taking aspirin. These other conditions can cause a "positive" result even when you don't have cancer.
• If your test is positive, you will probably need to have a colonoscopy.
• Unlike other tests, stool tests don't help prevent cancer by finding colon polyps before they turn into cancer. Stool tests mostly find cancer that is already present.

Flexible sigmoidoscopy (say "sig-moy-DAW-skuh-pee") is a test that lets your doctor look at the inside of the lower part of your colon. The doctor looks through a lighted tube that can bend around the corners of the colon.

With this test, the doctor can find polyps in the lower part of your colon and may be able to remove them. Polyps are growths inside the colon that can turn into colon cancer.

When used to screen for colon cancer, this test is usually done every 5 years.

Getting ready for a sigmoidoscopy involves cleaning out the colon:

• For 1 to 2 days before the test, you may be on a clear liquid diet.
• You will likely have an enema before the test.

This test usually takes 5 to 15 minutes or slightly longer if polyps are found and removed.

Risks of sigmoidoscopy

There is very little risk of problems from having a sigmoidoscopy.

• There is a slight chance of piercing the colon (perforation) or causing severe bleeding by damaging the wall of the colon. But this is rare.
• There is also a slight chance of a colon infection (very rare).

A sigmoidoscopy only looks at the lower part of your colon, which is where most polyps grow. But sometimes polyps grow in the upper part of your colon, and they would not be seen with this test.

If your doctor finds polyps during a sigmoidoscopy, you may need to have a colonoscopy to see if there are more polyps farther up in your colon.

Colonoscopy (say "koh-luh-NAW-skuh-pee") is a test that lets your doctor look at the inside of your entire colon . The doctor looks through a lighted tube that can bend around the corners of the colon.

With this test, the doctor can find and remove polyps, which are growths inside the colon that can turn into colon cancer.

When used as a screening test for colon cancer, this test is usually done every 10 years. If you have a colonoscopy, you won't need to have a yearly stool test. A colonoscopy may be done more often if your risk is higher than average.

Getting ready for a colonoscopy involves a very thorough cleansing of the colon, which must be completely empty:

• For 1 to 2 days before the test, you will be on a clear liquid diet.
• On the night before the test, your doctor may have you take a prescription laxative tablet or drink a laxative solution. This will make you use the bathroom often.

You may be given medicine to help you relax. Many people don't even remember the test afterward because they are so relaxed.

The test usually takes 30 to 45 minutes, but it may take longer if polyps are found and removed.

Risks of colonoscopy

The scope or a small tool may tear the lining of the colon or cause bleeding. Although these problems are rare, they happen more often with colonoscopy than with sigmoidoscopy.

Virtual colonoscopy

A virtual colonoscopy uses pictures taken during a CT scan to look at the colon. With this procedure, a thin tube is inserted into the rectum and air is pumped through the tube into the colon. The air expands your colon so that it is easier to see on an X-ray. If you are interested in learning more about virtual colonoscopy, talk to your doctor.

Getting ready for a virtual colonoscopy involves the same thorough cleansing of the colon that is needed for a regular colonoscopy:

• For 1 to 2 days before the test, you will be on a clear liquid diet.
• On the night before the test, your doctor may have you take a prescription laxative tablet or drink a laxative solution. This will make you use the bathroom often.

Virtual colonoscopy is still being studied to see if it works as well as a regular colonoscopy. If polyps are found, you will need a regular colonoscopy to have them removed.

*Based on the best available evidence (evidence quality: moderate)

Benefits

Colon cancer screening can help reduce cancer deaths. The quality of this evidence is moderate.

Take a group of 1,000 people ages 50 to 74.

• With a stool test every year, 10 people out of 1,000 will avoid death from cancer over their lifetimes, compared with people who do not have any screening.
• With a sigmoidoscopy every 5 years, 10 to 20 people out of 1,000 will avoid death from cancer over their lifetimes, compared with people who do not have any screening.
• With a colonoscopy every 10 years, 30 to 40 people out of 1,000 may avoid death from cancer over their lifetimes, compared with people who do not have any screening.

Risks

There is no risk involved in having a stool test.

Problems are rare with sigmoidoscopy. They are also rare with colonoscopy, but they happen more often with colonoscopy than with sigmoidoscopy. The quality of this evidence is moderate.

Take a group of 1,000 people .

• If all of them have a sigmoidoscopy, less than 1 person out of 1,000 will have a serious complication from the test, which could include death. This means that more than 999 out of 1,000 people will not have a serious problem.
• If each one has a colonoscopy, 2 to 3 people out of 1,000 will have a serious complication, which could include death. This means that 997 or 998 people out of 1,000 will not have a serious problem.

Understanding the evidence

Some evidence is better than other evidence. Evidence comes from studies that look at how well treatments and tests work and how safe they are. For many reasons, some studies are more reliable than others. The better the evidence is—the higher its quality—the more we can trust it.

The information shown here is based on the best available evidence.^{1, 2, 3, 4, 5, 6, 7} The evidence is rated using four quality levels: high, moderate, borderline, and inconclusive.

Another thing to understand is that the evidence can't predict what's going to happen in your case. When evidence tells us that 2 out of 100 people who have a certain test or treatment may have a certain result and that 98 out of 100 may not, there's no way to know if you will be one of the 2 or one of the 98.

Recommendations from the U.S. Preventive Services Task Force

• People ages 50 to 75 should have a fecal occult blood test (FOBT), sigmoidoscopy, or colonoscopy.
• People who have a sigmoidoscopy every 5 years should also have a stool test (FOBT) at regular intervals.
• Some people older than 75 may benefit from screening tests. Others may not. Talk to your doctor about continuing testing for colon cancer after age 75.

Recommendations from other groups

• The American Cancer Society (ACS), the American Gastroenterological Association (AGA), and the American College of Gastroenterologists (ACG) recommend routine testing for people age 50 and older who have a normal risk for colon cancer. Your doctor may recommend earlier or more frequent testing if you have a higher risk for colon cancer. Talk to your doctor about when you should be tested.