Colon and rectal cancer screening is a technique in which doctors check the colon and rectum for signs of cancer or growths (called polyps) that may become cancer. It is done in people who have no symptoms and no cause to believe they have cancer. The goal is to find and remove polyps before they become cancer, or to find cancer early, before it grows, spreads, or causes problems.
The colon and rectum are the end part of the digestive tract. When doctors speak about colon and rectal cancer screening, they use the term “colorectal.” That is just a shorter way of saying “colon and rectal.” It’s also possible to say just colon cancer screening.
- Colonoscopy– Colonoscopy allows the doctor to see directly inside the complete colon. Before you can have a colonoscopy, you must clean out your colon. You do this at home by drinking a special liquid that causes watery diarrhoea for several hours. On the day of the test, you get medicine to help you relax. Then a doctor puts a thin tube into your anus and advances it into your colon. The tube has a tiny camera attached to it, so the doctor can see inside your colon. The tube also has tiny tools on the end, so the doctor can remove pieces of tissue or polyps if they are there. After polyps or pieces of tissue are removed, they are sent to a lab to be checked for cancer.
- CT colonography(also known as virtual colonoscopy or CTC) – CTC looks for cancer and polyps using a special X-ray called a “CT scan.” For most CTC tests, the preparation is the same as it is for colonoscopy.
- Stool test for blood– “Stool” is another word for bowel movements. Stool tests most commonly check for blood in samples of stool. Cancers and polyps can bleed, and if they bleed around the time you do the stool test, then blood will show up on the test. The test can find even small amounts of blood that you can’t see in your stool. Other less serious situations can also cause small amounts of blood in the stool, and that will show up in this test. You will have to collect small samples from your bowel movements, which you will put in a special container you get from your doctor.
- Sigmoidoscopy– A sigmoidoscopy is similar in some ways to a colonoscopy. The difference is that this test looks only at the last part of the colon, and a colonoscopy looks at the whole colon. Before you have a sigmoidoscopy, you must clean out the lower part of your colon using an enema. This bowel cleaning is not as thorough or unpleasant as the one for colonoscopy. For this test, you are not required to take medicines to help you relax, so you can drive and work afterward if you want.
- Stool DNA test– The stool DNA test checks for genetic markers of cancer, as well as for signs of blood. For this test, you get a particular kit in order to collect a whole bowel movement. Then you follow the advice about how and where to ship it.
- There is no blood test that most experts think is accurate enough to use for screening.
Work with your doctor to decide which test is best for you. Some doctors might choose to combine screening tests, for example, sigmoidoscopy plus stool testing for blood. Being screened–no matter how–is more important than which test you choose.
Doctors suggest that most people begin having colon cancer screening at age 50. People who have an increased risk of getting colon cancer sometimes begin screening at a younger age. That may include people with a strong family history of colon cancer, and people with diseases of the colon called “Crohn’s disease” and “ulcerative colitis.”
Most people can stop being screened around the age of 75, or at the latest 85.
That depends on your risk of colon cancer and which test you have. People who have a high risk of colon cancer often need to be tested more often and should have a colonoscopy.
Most people are not at high risk, so they can decide one of these schedules:
- Colonoscopy every 10 years
- CT colonography (CTC) every 5 years
- Stool testing for blood once a year
- Sigmoidoscopy every 5 to 10 years
- Stool DNA testing every 3 years (but doctors are not yet sure of the best time frame for repeating the test)