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. Polyps are growths attached to the inside of the colon or rectum. Colon polyps are common. Most of them don't turn into cancer. Polyps are found during some screening tests. And polyps found during a colonoscopy usually can be removed at the same time.

With colorectal cancer, symptoms often don't show up until the cancer is advanced. So regular screening—no matter what test you choose—makes it more likely that cancer will be found early, when the cancer may be easier to treat. And colorectal cancer can be prevented if your doctor finds and removes polyps during a colonoscopy.

A family history of colorectal cancer makes you more likely to get it. You may need to be screened at an earlier age—and be tested more often—than other people if:

• You have a close relative with colorectal cancer. You are more likely to get colorectal 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 had it at any age.
• You have a family history of certain inherited gene changes. These include familial adenomatous polyposis (FAP) and Lynch syndrome. Most people who inherit these conditions will get colorectal cancer if they are not screened and treated.

Stool tests involve checking your stool for tiny amounts of blood or other signs of colorectal cancer.

Most stool tests need to be done once a year. These tests can usually be done in your home.

There are different types of stool tests:

• Fecal immunochemical test (FIT). This test checks for signs of blood in the stool. The test kit contains the things that you need for collecting small samples of stool. This test is recommended every year.
• Guaiac-based fecal occult blood test (gFOBT). This test also checks for signs of blood in the stool. The test kit contains the things that you need for collecting small samples of stool. With a gFOBT, you will be given instructions about foods to avoid in the days before the test. This test is recommended every year.
• Combined fecal immunochemical test and stool DNA (FIT-DNA). This test checks the stool for blood and genetic changes in DNA that could be signs of cancer. The test kit has a container for collecting an entire stool sample. This test is recommended every 1 to 3 years.

You can get an at-home stool test from your doctor or your local drugstore, or you can order one online. Your test kit will have instructions about how to do the test, including how to return your stool samples. Some tests provide the results right away. If your test shows a positive result (blood was found), call your doctor as soon as possible. You will need a colonoscopy.

Risks of stool tests

There is no risk from the stool test itself. For this test, you put a sample of stool on a card or you collect a stool sample.

But there are some important things to think about. If your test is positive, you will need to have a colonoscopy. This would be used to see if the stool test result is from colorectal cancer. But blood in the stool is more often caused by something other than cancer. These other causes could include hemorrhoids, ulcers, or taking aspirin. A positive test result could lead you to worry. And you might have a colonoscopy only to find out that you didn't have cancer after all.

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 colorectal cancer.

When used as a screening test for colorectal 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 ("colon prep"). The colon 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 large container of laxative solution. This will make you use the bathroom often.
• If your doctor ordered a split prep, you'll do part of the prep the evening before and the other part on the day of the test.

During the test, you may be given medicine to help you relax. Many people don't 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

There is a small chance for problems from having a colonoscopy. The scope may tear the lining of the colon or cause bleeding.

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.

When used to screen for colorectal cancer, this test is usually done every 5 years. Or you can have the test every 10 years if you also do the FIT stool test every year.

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 use an enema or laxative (or both) to empty the colon before the test.

This test usually takes 5 to 15 minutes.

Risks of sigmoidoscopy

There is a small 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 very rare chance of a colon infection.

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. Those polyps would not be seen with this test.

If your doctor finds polyps during a sigmoidoscopy, you will need to have a colonoscopy to see if there are more polyps farther up in your colon. And that test also has possible risks.

CT colonography uses pictures taken during a CT scan to look at the colon. A thin tube is inserted into the rectum, and air is pumped through the tube into the colon. The air expands the colon so that it is easier to see on an X-ray.

When used as a screening test, it is usually done every 5 years.

Getting ready for this test involves the same cleansing of the colon that is needed for a regular colonoscopy.

If anything is found during the CT scan, you may need to have more tests, such as a colonoscopy, to make sure that you don't have cancer.

Risks of CT colonography

There is a very small risk that the lining of the colon may be injured or torn when air is pumped into the colon. This may cause bleeding.

CT colonography may find things outside the colon that might never have caused a problem if they had not been found through screening. But this test can't tell whether the problem is harmless. So you may need more tests or treatment. This can cost a lot and cause worry.

You will be exposed to radiation during this test. There is a small chance of getting cancer from having repeated CT colonographies or exposure to radiation from other sources, such as CT scans.

Your risk for colorectal cancer gets higher as you get older. Experts recommend starting screening at age 45 for people who are at average risk.^{footnote 1} Talk with your doctor about your risk and when to start and stop screening.