QUICK SUMMARY Why it's important: Colorectal cancer is the third most common type of cancer, and screening can help detect it in the early stage or before it develops. Who needs it? Men and women ages 50 to 75; people younger than age 50 who have certain risk factors. Good to Know: Don’t wait too long between screenings; the timing is meant to catch potential problems early. What is colorectal cancer screening? |
A colorectal cancer screening is a way to look for cancer or precursors to cancer in the colon (large intestine) or rectum (the last part of intestines before the anus) before symptoms emerge. Experts recommend four ways to screen in this area — colonoscopy and sigmoidoscopy, which look inside the colon and rectum; a virtual colonoscopy, also known as a CT colonography; or tests that look for blood and/or altered DNA in stool (poop), which may be a marker of cancer. |
Why is it important? |
Colorectal cancer is the third most common type of cancer and the second leading cause of cancer death in the US. |
Colorectal cancer almost always starts as small lumps called polyps that can turn into cancer over time. It's best to find these early, before they have a chance to become cancer. Early stage colorectal cancer may not have symptoms, so if there is already cancer in the colon or rectum, screening tests can detect it early — when treatment works best and offers the best chance for a cure. |
Who needs it? |
The U.S Preventive Services Task Force says that all men and women 50 to 75 with an average risk of colorectal cancer should have regular screenings. (The American Cancer Society recommends starting screening a bit earlier, at age 45.) Adults over age 76 may not need routine screening, so ask your doctor for advice. |
People with certain risk factors may need to start their screenings before age 50, and they may need to be screened more often than people of average risk. Risk factors can include digestive disorders such as inflammatory bowel disease (IBD), a previous adenomatous polyp, a prior colorectal cancer, or a family history of colorectal cancer. |
What to expect |
You should talk with your doctor to choose the right screening test for you. You may also want to talk about the pros and cons of each test — including the preparation and time it takes, potential risks, the cost, and your insurance coverage. |
Here's what you can expect for each test: |
Colonoscopy (every 10 years): This is the most thorough test, so you may not need to repeat it as often as other screening tests. Because it's so thorough, it can also be used as a follow-up if another screening test finds something unusual. Before your procedure you'll need to clear out your entire colon with laxatives recommended by your doctor (usually the night before and the morning of the test). Typically you'll be sedated or “put under” with drugs, so you'll need to arrange a ride home afterward. |
During the test you'll be given medicine so you shouldn't feel any pain (depending on the drug, you may feel relaxed or totally “out”). You'll lie on your side and the doctor will insert something called an endoscope into your rectum. (Endoscopy means “to look inside.”) The scope is a thin, flexible tube that's long enough to travel through the entire colon (the whole thing is about five feet long). It has a light and camera so that your doctor can see inside. |
The scope is pushed all the way to the beginning of your colon. As it's pulled back out, your doctor will look at your colon walls. Any polyps or tumors may be taken out or sampled (called a biopsy). The test itself generally takes about 30 to 60 minutes, or longer if polyps are removed. You'll probably need to take it easy for the rest of the day, and may feel bloating or cramps. |
In rare cases, the test can cause infections or bleeding (especially if polyps were removed). Rarely, the scope can also poke through (perforate) the colon wall during a colonoscopy, which may need to be repaired with surgery. |
If everything looks good, you shouldn't need another colonoscopy for 10 years. |
Sigmoidoscopy (every 5 years): This is like a “light” colonoscopy because it checks only the last one-third of the colon and rectum. As with a colonoscopy, you'll need to clear out your system with laxatives before this test. Sedation is usually recommended. You might be given a mild sedative in pill form or a sedative combined with an intravenous pain medication to ease any discomfort. |
During the test, you’ll lie on your side and the doctor will insert an endoscope (a thin, flexible, lighted tube) into your rectum to look for polyps or cancer in the rectum and the lower part of the colon. (This lower third is called the “sigmoid” or “S-shaped” colon.) |
You may feel pressure and some cramping during the test. If there are small polyps, your doctor may take them out for biopsy. The test generally takes about 15 minutes. Afterward, you may feel some bloating or cramps, but you'll probably be able to go about the rest of your day. |
In rare cases, the test can cause infections or bleeding (especially if polyps were removed). Rarely, the scope can also poke through (perforate) the colon wall during a sigmoidoscopy, which may need to be repaired with surgery. |
If you have a clean sigmoidoscopy, experts say you should have your next one in five years. Some doctors may also recommend stool tests in the interval. Another approach to consider is having a sigmoidoscopy every 10 years along with a stool test, which may be a good option for patients who want to avoid a colonoscopy. |
Stool test (every year or every three years, depending on type): There are three types of stool tests that check for small amounts of blood in your poop. These quick tests are less intrusive, but they are not as definitive as the tests that look at the colon directly, so they need to be repeated more often. The guaiac-based fecal occult blood test (gFOBT) uses the chemical guaiac to detect blood in your stool. The fecal immunochemical test (FIT) uses antibodies to detect blood in the stool. The FIT-DNA test combines the FIT test with one that detects altered DNA in the stool. |
For the gFOBT and FIT tests, you'll take home a kit from your doctor or lab. When you go to the bathroom, you'll swab a small sample from your stool with a little brush or stick and package it in the kit. Then you'll return the kit to your doctor or lab, and they'll check the sample for blood that can signal cancer. With a FIT-DNA test, you’ll need to collect an entire bowel movement to send to a lab for it to be checked for cancer cells. The gFOBT and FIT tests are recommended every year, while the FIT-DNA test can be done every one to three years. If the results are abnormal this test may be followed by a colonoscopy. Virtual colonoscopy (every five years): With a virtual colonoscopy, also known as a CT colonography, a radiologist uses an X-ray and a computer to create images of your rectum and colon. A virtual colonoscopy can detect ulcers, polyps, or cancer. It’s potentially not as effective at finding certain polyps as a regular colonoscopy. It's usually used as a screening tool to look for polyps or cancer or in cases where a colonoscopy was incomplete or couldn’t be done. To prepare for a virtual colonoscopy, you’ll have to change your diet, clean out your bowel with laxatives and drink a special liquid called contrast medium the night before. The contrast medium shows up on X-rays and helps your doctor tell the difference between polyps and stool. Unlike with a colonoscopy, you won’t need anesthesia. For the test, you’ll lie on a table while an X-ray technician inserts a thin tube through your anus and into your rectum. The tube inflates your large intestine with air to allow for better X-ray images. The table slides into a CT machine where the X-ray images are taken. You may be asked to hold your breath a few times and you will be asked change positions, such as moving onto your side or stomach. The test takes about 10 to 15 minutes. For the first hour after the test, you might experience cramping or bloating. Otherwise, you can return to your normal diet or activities right away. The radiologist will look at your test images for possible problems and send a report to your doctor. If there are any problems, you might undergo a colonoscopy the same day or at a future date. If your results are normal, your doctor might recommend you have another exam in five years. A virtual colonoscopy does come with a slight risk that the lining of your large intestine could be perforated when your colon is inflated with air. In that case, it would be repaired with surgery. |
Good to know |
Even though it might not be your favorite thing in the world, don't wait too long between screenings. The time between tests is designed to catch problems early (one to 10 years, depending on the test and your personal risk factors). Depending on the results of your tests, your doctor may want you to be screened more often. |
Selected references |
National Cancer Institute. Tests to Detect Colorectal Cancer and Polyps. Last reviewed July 2016. Centers for Disease Control and Prevention. Colorectal Cancer. Last reviewed February 2019. U.S. Preventive Services Task Force (USPSTF). Colorectal Cancer: Screening. Last updated June 2017. |
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