When should I get screened for colorectal cancer? What screenings do I need?

Colorectal cancer is a major threat to the health of Americans; it is the third-most-common cancer diagnosed in both men and women, and the second-leading cause of cancer deaths in the U.S. The lifetime risk of being diagnosed with colorectal cancer is about 1 in 25, and the lifetime risk of dying from it is about 1 in 55.

The good news is that it is also one of the most preventable causes of cancer death. Screening for colorectal cancer can be highly effective at preventing cancer, as well as finding cancer at an early stage, when there is a much better chance at a cure. For screening to work, however, it must be done before you develop symptoms of cancer, such as blood in the stool, unexplained abdominal pain, new constipation, narrowing of stool shape or unexplained weight loss.

Although there is some disagreement among experts as to when to begin screening, all experts agree that everyone should begin screening by age 50. In the past few years, we have seen an unprecedented increase in colorectal cancer among young adults, which many experts believe is related to the high-fat, low-fiber American diet and to the obesity epidemic. In 2018, the American Cancer Society lowered the recommended starting age for screening to 45 in average-risk adults, but the U.S. Preventive Services Task Force still recommends starting screening at age 50.

Some folks are at higher risk for colorectal cancer than others. Those with a family history of colorectal cancer or advanced polyps (pre-cancerous growths), particularly in a parent, sibling or child, are at especially high risk. People in these groups should start screening 10 years before the age at which their family member was diagnosed, or at age 40, whichever is earlier. Other risk factors for colorectal cancer include smoking; heavy alcohol consumption; a diet high in meat and low in fruits, vegetables and whole grains; physical inactivity; and obesity. African-Americans are also at higher risk for colorectal cancer.

There are several excellent options for colorectal cancer screening. The most commonly performed test in the U.S. is colonoscopy, which is a flexible tube with a camera allowing examination of your entire colon. It can detect and remove polyps before they become cancer, and, accordingly, is the best screening test to prevent cancer. The downsides: it requires a powerful laxative to completely clean out the bowels, a day off from work, and a companion to accompany you, since a sedative is usually used. There is also a very small risk of perforating the bowel and causing bleeding. Colonoscopy is done every 10 years if no polyps are detected.

There are several stool-based tests that are excellent at detecting colorectal cancer before it causes any symptoms. The fecal immunochemical test (FIT) and the high-sensitivity guaiac test look for tiny amounts of blood that can be the first sign of cancer. A newer stool test called FIT-DNA detects both blood and genetic material shed in the stool by the cancer. These tests are done in the convenience of your own home, take very little time and no significant preparation. The disadvantage is that they don’t do a good job detecting pre-cancerous polyps, so that while they are excellent at detecting cancer, they are not as good at preventing cancer. The FIT and guaiac tests are done yearly and the FIT-DNA is done every three years. If the test is abnormal, your doctor will arrange a follow-up colonoscopy.

A newer test called CT colonography, or “virtual colonoscopy,” uses CT scanning to create a 3-D image of your entire colon. It is excellent at finding cancer and larger polyps. The advantages over colonoscopy are that it doesn’t require sedation and is safer. However, you do need to complete the same bowel prep as for colonoscopy. If an abnormality is detected, you’ll need a colonoscopy, which likely means another bowel prep, unless your hospital has same-day colonoscopy. Also, some insurance providers, including Medicare, don’t cover CT colonoscopy. This test is done every five years.

So which test is right for you? If the idea of preventing cancer by finding and removing polyps is particularly appealing, and you don’t mind a powerful laxative and a day off work, colonoscopy is probably the way to go. If ease and convenience are more important, stool testing is probably the best bet. Just remember that the best test by far is the one that gets done. So if you’re one of the 40% of Americans not up to date with colorectal cancer screening, talk with your healthcare provider about which test is right for you — and get tested.

Dr. Andrew M.D. Wolf is a general internist at UVa Health System. He was first author of the American Cancer Society’s 2018 Colorectal Cancer Screening Guideline. 

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