Colorectal Cancer Screening

For average-risk patients, screening for colorectal cancer (CRC) should begin at age 45 years and continue until age 75 years. For adults aged 76 to 85, the decision whether to screen for CRC should be individualized, taking into consideration the patient's overall health and prior screening history (1–4).

There are multiple options for CRC screening, including

• Colonoscopy every 10 years

• Fecal occult blood test annually (fecal immunochemical tests [FIT] preferred)

• Flexible sigmoidoscopy every 5 years (every 10 years if combined with FIT)

• CT colonography every 5 years

• Fecal DNA testing combined with FIT, at least every 3 years

The American College of Gastroenterology (ACG) 2021 colorectal cancer screening guidelines recommend colonoscopy every 10 years or annual FIT as the preferred screening tests (2).

Colonoscopy is considered the gold standard screening test. Alternative CRC screening tests are available for patients who decline colonoscopy or for whom economic issues preclude screening with colonoscopy and for whom the need for repeated testing with FIT is problematic. Patients with a family history of a first-degree relative with CRC diagnosed prior to age 60 should undergo colonoscopy every 5 years, beginning at age 40 years, or 10 years before the age the relative was diagnosed, whichever comes first. Screening of patients with high-risk conditions (eg, ulcerative colitis) is discussed under the specific condition.

Fecal immunochemical tests (FIT) for blood are more sensitive and specific for human blood than older guaiac-based stool tests, which can be affected by many dietary substances. However, a positive test for blood can result from nonmalignant disorders (eg, ulcers, diverticulosis), and a negative test result does not exclude cancer because cancers do not bleed continuously. Newer high-sensitivity guaiac fecal occult blood tests may be an acceptable alternative.

Fecal DNA testing detects DNA mutations and methylation markers shed from a colonic tumor. The test typically is combined with FIT, and the combined test is approved for screening average-risk patients. Patients with a positive fecal DNA-FIT test should get a follow-up colonoscopy within 6 months to reduce the risk of missing advanced colon cancer. Approximately 10 to 15% of patients with a positive fecal DNA-FIT test result have a normal colonoscopy; such patients can have a repeat fecal DNA-FIT test in 1 year or a repeat colonoscopy in 3 years. If these tests are negative, they can return to the average-risk colon cancer screening schedule.

CT colonography (virtual colonoscopy) generates 3D and 2D images of the colon using multidetector row CT and a combination of oral contrast and gas distention of the colon. Viewing the high-resolution 3D images somewhat simulates the appearance of optical endoscopy, hence the name. It has some promise as a screening test for people who are unable or unwilling to undergo endoscopic colonoscopy but is less sensitive and highly interpreter-dependent. It avoids the need for sedation but still requires thorough bowel preparation, and the gas distention may be uncomfortable. Additionally, unlike with optical colonoscopy, lesions cannot be biopsied during the diagnostic procedure.

Video capsule endoscopy of the colon has many technical problems and is not preferred but is sometimes considered an acceptable alternative screening test.

Blood-based tests (eg, Septin 9 assay) have been approved for screening average-risk patients but are not widely used because of inadequate sensitivity; they are not recommended in the ACG guidelines.