colorectal cancer screening

overview

Cancers of the colon and rectum (colorectal cancers) are some of the most preventable because screening tests can detect growths before they become cancerous. Most often, colon cancer happens in the lower part of the colon. Cancer in the rectum is called rectal cancer. Colorectal cancers start out as growths (polyps) on the lining of the colon. Polyps are usually noncancerous when they first appear, and over time can turn into cancerous polyps (adenoma). Removal of these polyps can reduce the risk of colon cancer by more than 80%. 

The gold standard for colorectal cancer screening is a colonoscopy. This test examines the entire colon, and your doctor can remove any polyps found during the test. There are other screening options, such as flexible sigmoidoscopy, double-contrast barium enema, virtual colonoscopy (CT colonography) and fecal occult blood test (FOBT).

It’s recommended that all adults get their first colorectal cancer screening at age 50, or earlier if there’s a family history or medical condition that puts you at a higher risk.

colonoscopy

In a colonoscopy, the entire length of your large intestine and colon is examined, and polyps and cancer are detected and removed. If your first colonoscopy doesn’t detect a problem, you won't need another one for 10 years.

What to expect
For the test to be effective, you have to empty your colon completely beforehand. For the day before, you’ll eat no food and drink only clear liquids. You’ll take a laxative (in liquid or pill form) and, if needed, give yourself an enema. On the day of the test, you’ll be given sedation meds through a needle in your arm (IV) to relax you. While you’re lying on your side, your doctor inserts a long, flexible tube containing a camera through your anus and into your rectum and colon. This allows your doctor to see inside your large intestine and colon. Any polyps can be removed using tools inserted through the tube. Your doctor can also collect tissue samples (biopsy) to check for cancer. The whole procedure takes about 30 minutes. Because you’ve been sedated, you won’t be able to drive, so you'll need to arrange for a ride home.
 
If any of the following screening tests detect abnormalities, your doctor may recommend you have a colonoscopy.

flexible sigmoidoscopy

This test checks only the lower third of the colon, and it can detect polyps and cancer. It’s recommended every 5 years.

What to expect
For the test to be effective, you have to empty your colon completely beforehand. For the day before, you’ll eat no food and drink only clear liquids. You’ll take a laxative (in liquid or pill form) and if needed give yourself an enema. On the day of the test, you won’t usually receive sedation meds. Your doctor inserts a long tube (sigmoidoscope) containing a camera through your anus and into your rectum and lower colon. This allows your doctor to see inside your lower colon. If polyps are detected, they can be removed with tools inserted through the tube. Your doctor can also collect tissue samples (biopsy) to check for cancer. The whole procedure takes about 15 minutes, or longer if polyps are detected.

double-contrast barium enema

This test can detect large polyps and cancer and is recommended every 5 years.

What to expect
For the test to be effective, you have to empty your colon completely beforehand. For the day before, you’ll eat no food and drink only clear liquids. You’ll take a laxative (in liquid or pill form) and, if needed, give yourself an enema. On the day of the test, you’ll have an enema with a barium solution and an injection of air through a tube inserted in your anus. The barium coats the lining of your intestines, which helps polyps and other abnormalities show up better on a series of X-rays taken of your rectum and colon.

virtual colonoscopy (CT colonography)

This test can detect polyps and cancer, and might be right for you if you can’t have colonoscopy. It’s recommended every 5 years.

What to expect
For the test to be effective, you have to empty your colon completely beforehand. For the day before, you’ll eat no food and drink only clear liquids. You’ll take a laxative (in liquid or pill form) and, if needed, give yourself an enema. On the day of the test, you’ll lie on your side with your knees pulled toward your chest. Your doctor inserts a tube into your anus and pumps air through it to make your colon easier to see. Then you’ll have CT (computed tomography) scans to produce pictures of your colon. You’ll lie on your back and your stomach so your doctor can get images from different angles. Scans are reviewed to check for abnormalities.

fecal occult blood test FOBT

This test can detect cancer and is recommended once a year.

What to expect
You may have to avoid certain foods for a few days before a FOBT, which is a lab test that looks for hidden (occult) blood in your stool. Depending on the type of test or kit that’s used, you may have to provide stool samples from one or several bowel movements to your doctor or to a mail-in lab.

stool DNA test

This test detects cancer, and there’s not yet a recommended amount of time between tests. It could be between 2 and 5 years.

What to expect
There’s no special preparation necessary. This is a new lab test that checks stool for DNA changes. Your doctor gives you a kit, and you provide a stool sample to your doctor or to a mail-in lab.

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