Colorectal Cancer Screening

Colorectal cancer screening tests adults without symptoms to detect colorectal cancer early and, in the case of endoscopic methods, to find and remove the adenomatous polyps from which most colorectal cancers arise. Because it can both detect early cancer and remove precursors, it can lower both colorectal cancer mortality and incidence.

Definition

Colorectal cancer screening is the application of stool-based or structural (endoscopic or imaging) tests to asymptomatic adults to detect colorectal cancer early and, where polyps are found and removed, to prevent cancer.

Scope

This topic covers the principal screening strategies, stool-based tests such as faecal occult blood and faecal immunochemical testing, structural examinations such as sigmoidoscopy and colonoscopy, and newer stool-DNA tests, together with the trial and review evidence on their effect on mortality and incidence. It is a reference account of the modalities and evidence, not individual screening advice.

Core questions

• How do stool-based and endoscopic screening strategies differ in their effect on colorectal cancer mortality and incidence?
• How does removal of adenomatous polyps reduce later cancer incidence?
• How do test performance, acceptability and interval shape the value of a screening programme?

Key concepts

• Adenoma-carcinoma sequence
• Faecal occult blood test (gFOBT)
• Faecal immunochemical test (FIT)
• Sigmoidoscopy and colonoscopy
• Polypectomy
• Multitarget stool DNA test
• Incidence versus mortality reduction

Mechanisms

Most colorectal cancers develop slowly from adenomatous polyps through the adenoma-carcinoma sequence, providing a long window for detection. Stool-based tests detect occult blood (guaiac-based gFOBT or the more specific immunochemical FIT) or abnormal DNA shed by neoplasia, identifying people who should proceed to colonoscopy. Repeated faecal occult blood testing reduces colorectal cancer mortality by bringing cancers to diagnosis earlier (Hewitson, 2007). Endoscopic screening goes further: at sigmoidoscopy or colonoscopy, precursor polyps can be removed during the same procedure, so structural screening reduces not only mortality but the incidence of colorectal cancer (Brenner, 2014).

Clinical relevance

Colorectal screening is a core primary-care and public-health preventive activity, and guideline bodies describe eligible ages, acceptable test options and intervals for average-risk adults (USPSTF, 2021). This entry summarizes the comparative evidence for reference; it makes no recommendation for any individual and specifies no test choice or interval for a given person.

Epidemiology

Randomized trials of guaiac faecal occult blood testing established a reduction in colorectal cancer mortality, and meta-analyses of sigmoidoscopy and colonoscopy show reductions in both incidence and mortality attributable to detection and removal of precursors (Hewitson, 2007; Brenner, 2014). A large randomized comparison found that FIT and colonoscopy achieved similar detection of cancer with differing participation and detection of advanced adenomas, informing the use of multiple acceptable strategies (Quintero, 2012).

History

Trials of guaiac-based faecal occult blood testing in the 1980s and 1990s were the first to show that colorectal screening reduces cancer mortality. Endoscopic approaches followed, with randomized sigmoidoscopy trials and meta-analyses demonstrating reductions in incidence through polypectomy (Brenner, 2014). More recent developments include the more specific faecal immunochemical test, head-to-head comparison of FIT with colonoscopy (Quintero, 2012), and multitarget stool-DNA testing (Imperiale, 2014), broadening the menu of acceptable strategies.

Debates

Stool-based versus endoscopic screening as the preferred strategy

Stool-based tests are non-invasive and achieve higher participation but require follow-up colonoscopy for positives and detect fewer precursor adenomas, while colonoscopy can prevent more cancers through polypectomy at the cost of invasiveness; programmes weigh these trade-offs differently, and several strategies are regarded as acceptable.

Key figures

• Paul Hewitson
• Hermann Brenner
• Enrique Quintero
• Thomas Imperiale

Seminal works

• hewitson-2007
• brenner-2014

Frequently asked questions

How can colorectal screening lower cancer incidence and not just mortality?

Most colorectal cancers arise from adenomatous polyps over many years; at sigmoidoscopy or colonoscopy these polyps can be removed before they become cancer, so endoscopic screening can reduce the number of cancers that occur, not only deaths from them.

What is the difference between gFOBT and FIT?

Both detect blood in the stool, but the guaiac-based test (gFOBT) relies on a chemical reaction and can be affected by diet, whereas the faecal immunochemical test (FIT) uses antibodies specific to human haemoglobin, making it more specific and easier to use.