Screening for colorectal cancer decreases the risk of cancer spread and dying of colorectal cancer

Fitzpatrick-Lewis D, Ali MU, Warren R, et al. Screening for colorectal cancer: A systematic review and meta-analysis Clinical Colorectal Cancer. 2016;15:298-313.

Review question

Do colorectal cancer screening tests decrease the risks of dying, dying specifically from colorectal cancer and developing widespread cancer? How likely are each of these tests to cause harm? Are people of certain ages more likely to benefit from or be harmed by colorectal cancer screening?

Background

Colorectal cancer is one of the most common cancers in the world. Current guidelines recommend colorectal cancer screening for people aged 50 – 75 years. Cancer screening helps to diagnose cancer earlier and early diagnosis is more likely to result in successful treatment, stop cancer from spreading to other parts of the body and prevent cancer deaths. There are several colorectal screening tests available, including fecal occult blood testing (FOBT), sigmoidoscopy, colonoscopy and CT colonography. The aim of this review was to update guidelines for colorectal cancer screening and measure the benefits and harms of various colorectal screening tests.

How the review was done

This is a systematic review and meta-analysis of 55 studies (including 9 randomized controlled trials) conducted from January 2000 to February 3, 2015.

• All participants were adults aged 18 years or older who did not have symptoms of colorectal cancer and were not at high risk for colorectal cancer.
• Study participants took part in colorectal cancer screening using fecal occult blood tests (FOBT), flexible sigmoidoscopy, colonoscopy and/or CT colonography.
• 9 studies (953,154 participants) measured rates of death from any cause, death from colorectal cancer and development of late stage (widespread) cancer five to twenty years after the screening tests.
• 46 studies (413,435 participants) measured harms caused by the screening tests (such as bleeding and perforation of the colon) and inaccurate results (false positives and false negatives).
• Results were compared to control groups who did not receive colorectal cancer screening.

What the researchers found

People who were screened with FOBT and flexible sigmoidoscopy were less likely to die from colorectal cancer or develop widespread cancer. Screening was more likely to prevent risk of death from colorectal cancer for older participants (60 years and older). This review could not make any conclusions about the benefits of screening with colonoscopy or colonography since there were no randomized control trials available on the topic.

Screening with FOBT has a greater risk of false positive results, which can cause people to unnecessarily undergo more invasive testing. Flexible sigmoidoscopy was more likely to cause colon perforation, bleeding and death in some participants. Colonoscopy was even more likely to cause these types of complications. CT colonography had some risk of causing perforation.

Given related risks of screening, the review authors propose targeted screening for older people and people at high risk for colon cancer, as the harms may outweigh the benefits for younger adults.

Conclusion

FOBT and flexible sigmoidoscopy are both effective screening tests for colorectal cancer as they decrease the risk of cancer spread and death from cancer. People aged 60 and older are likely to benefit more from colorectal cancer screening tests. Risk of harms from screening may outweigh the benefits for younger people and/or people at lower risk of colorectal cancer.