Colorectal cancer is the third leading cancer killer of males and females in the United States. In August 2021, the U.S. Preventive Services Task Force updated its colorectal screening guidelines to include adults aged 45-49 (Grade B recommendation). Grade A recommendation for those 50-75. For adults 76 to 85, a Grade C recommendation is in place for providers to selectively offer colorectal screening to patients, noting that providers should consider a patient's overall health condition, whether or not they have previously been screened for colorectal cancer, as well as the patient's desire. 

Screening intervals for colorectal cancer are a little complicated as there are multiple tests and technologies involved. The recommended screening options are:

     -Colonoscopy screening every ten years.

     -Flexible sigmoidoscopy every ten years if yearly

      fecal immunochemical test (FIT) is also performed.

     -Flexible sigmoidoscopy every five years.

     -CT colonography every five years.

     -FIT-DNA test every 1 to 3 years.

     -High-sensitivity guaiac fecal occult blood test (gFOBT) or FIT every year.

The sensitivity of colonoscopy to detect adenomas 10 mm or larger is reported to be between 89-95%, with a specificity of 89%. The USPSTF did not find any studies that reported the sensitivity and specificity of flexible sigmoidoscopy compared to colonoscopy. The sensitivity of CT colonography to detect colorectal cancer or adenomas 10 mm or larger was 86-100%. The sensitivity of FIT-DNT tests to detect colorectal cancer was 93%, with a specificity of 84%. To detect adenomas 10 mm or greater, FIT-DNA tests sensitivity were 43%, with a specificity of 89%. The sensitivity of high-sensitivity gFOBT to detect colorectal cancer and adenomas 10 mm or greater was 50-100%, with a specificity of 96-98%. The sensitivity of FIT to detect colorectal cancer was 74%, with a specificity of 93-96%. To detect adenomas 10 mm or greater, FIT sensitivity was 23%, with a specificity of 96%. 

Colorectal cancer is advantageous for screening because pre-cancerous polyps (adenomas) can be detected and subsequently removed. Therefore, colorectal screening is also a cancer prevention method by identifying and treating pre-cancerous lesions in conjunction with cancer screening. Indeed, colorectal has been found to reduce mortality from colorectal cancer by detecting cancer early. FIT screening was associated with a 10% decreased colorectal cancer mortality. A 2018 study in the journal Gut reported a 67% reduction in colorectal cancer mortality with screening colonoscopy. Flexible sigmoidoscopy has demonstrated a 26% decrease in colorectal mortality compared with no screening. Mortality data regarding screening with high-sensitivity gFOBT was not available in the JAMA report summarizing the USPSTF colorectal guidelines. However, an older gFOBT was associated with a 9-22% decrease in colorectal mortality. Positive screenings with flexible sigmoidoscopy or CT colonography require follow-up colonoscopy, as do non-visual (high-sensitivity gFOBT, FIT, and FIT-DNA test) positive screenings. 

References:

US Preventive Services Task Force, Davidson KW, Barry MJ, Mangione CM, et al. (2021). Screening for Colorectal Cancer: US Preventive Services Task Force Recommendation Statement. JAMA, 325(19), 1965–1977.

Doubeni CA, Corley DA, QuinnVP et al. (2018). Effectiveness of screening colonoscopy in reducing the risk of death from right and left colon cancer: a large community-based study. Gut, 67(2), 291–298.