Modalities

Colorectal cancer (CRC) screening modalities fall into two broad categories: direct visualization of the colon and stool testing. Stool testing, involving chemical analysis of fecal matter for blood and/or other molecular markers of abnormal cell growth,1 is a less invasive screening option.2 The risks and benefits of different screening tests vary, and clinicians may consider a variety of factors in deciding which test may be best.3 Stool tests are only appropriate for average risk patients.1

STOOL-BASED TESTS: EFFICACY AND CONSIDERATIONS3

METHOD EVIDENCE OF EFFICACY OTHER CONSIDERATIONS
High-Sensitivity gFOBT
  • RCTs have shown a reduction in CRC mortality
  • High-sensitivity versions perform better than older tests, but there is uncertainly about the precision of test sensitivity estimates. Given the uncertainty, it is unclear whether gFOBT can detect fewer cases of advanced adenomas and CRC than other stool-based tests
  • Harms from screening arise from colonoscopy to follow-up abnormal results
  • Requires good adherence over screening program
  • Does not require bowel preparation, anesthesia, or transportation to and from the screening examination (test performed at home)
  • Positive results require follow-up with colonoscopy for screening benefits to be achieved
FIT 
  • Large cohort study showed a reduction in CRC mortality
  • Certain types of FIT are more accurate than gFOBT or HSgFOBT
sDNA-FIT
  • Improved sensitivity compared to FIT per one-time application of screening test
  • Lower specificity than FIT, which results in more false positives and thereby more follow-up colonoscopies (and adverse events associated with colonoscopies) per sDNA-FIT screening test compared with per FIT test
  • Modeling suggests screening every 3 years is not optimal in terms of benefits and harms compared to annual FIT or sDNA-FIT every 1 or 2 years
  • Insufficient evidence on appropriate follow-up of abnormal findings after negative follow-up colonoscopy
 

SENSITIVTY AND SPECIFICITY OF SCREENING TESTS3

TEST SENSITIVITYf  SPECIFICITYf
 High-sensitivity gFOBT (CRC)a  0.50-0.75  0.96-0.98
 FIT (CRC)b  0.74g  0.94g
 sDNA-FIT(CRC)c  0.93g  0.84g
 Colonoscopy (adenomas 10mm or
larger)d
 0.89-0.95   0.89
CT Colonography (CRC)e
 0.86-1.0
  Not reported
CT Colonography (adenomas 10mm or
larger)e
 0.89g
  0.94g

  • Stool tests require no bowel preparation, no sedation, and are non-invasive2
  • The Unites States Preventive Services Task Force guidelines note that for sDNA-FIT, there is insufficient evidence about appropriate longitudinal follow up of abnormal findings after a negative diagnostic colonoscopy, and there is no direct evidence evaluating effect of sDNA-FIT on CRC mortality3
  • All positive results on non-colonoscopy screening tests should be followed up with a timely colonoscopy1,3-5
  • The recommendations note that there is no direct evidence evaluating the effect of CT colonography on CRC mortality; there is limited evidence about the potential benefits or harms of possible evaluation and treatment of incidental extracolonic findings, which are common3
  • Extracolonic findings are detected in 1.3% to 11.4% of exams, but ≤3% required medical or surgical treatment3

DIRECT VISUALIZATION: EFFICACY AND CONSIDERATIONS3

METHOD EVIDENCE OF EFFICACY  OTHER CONSIDERATIONS
 Colonoscopy
  •  Evidence from cohort studies that colonoscopy reduces CRC mortality
  • Harms from colonoscopy include bleeding and perforation, which both increase with age
  • Screening and diagnostic follow-up of positive results can be performed during the same examination
  • Requires less frequent screening
  • Requires bowel preparation, anesthesia, and transportation
  CT Colonography
  • Evidence available that CT colonography has reasonable accuracy to detect CRC and adenomas
  • Limited evidence about the potential benefits or harms of possible evaluation and treatment of incidental extracolonic findings, which are common
  • Potential harms from colonoscopy to follow up abnormal results
  • Requires bowel preparation
  • Does not require anesthesia or transportation
Flexible Sigmoidoscopy
  • RCTs have shown a reduction in CRC mortality
  • Risk of bleeding and perforation (less than with colonoscopy)
  • Modeling suggests fewer life-years gained alone than when combined with FIT or in comparison to other strategies
  • Potential harms from colonoscopy to follow up abnormal results
  • Test availability has declined in the US but may be available in some communities where colonoscopy is less available
Flexible Sigmoidoscopy with FIT
  • RCTs have shown a reduction in CRC mortality
  • Modeling suggests combination testing provides similar benefits to colonoscopy with fewer complications
  • Risk of bleeding and perforation (less than with colonoscopy)
  • Additional harms from colonoscopy to follow-up abnormal results
  • Test availability has declined in the US but may be available in some communities where colonoscopy is less available
  • Screening with FIT requires good adherence over multiple rounds of testing

ESTIMATED COMPLICATIONS OF CRC SCREENING AND FOLLOW-UP PROCEDURES PER 1000 INDIVIDUALS SCREENED (2021)3,h,i

  • Harms from stool-based screening arise from colonoscopy to follow-up abnormal results3

Related Topics

CT: computed tomography. FIT: fecal immunochemical test. gFOBT: guaiac-based fecal occult blood test. RCT: randomized controlled trial. sDNA: stool DNA. SIG: sigmoidoscopy.

References

1 Wolf AMD, Fontham ETH, Church TR, et al. Colorectal cancer screening for average-risk adults: 2018 guideline update from the American Cancer Society. CA Cancer J Clin. 2018;68(4):250-281.

2 American Cancer Society. Colorectal cancer screening tests. Updated June 29, 2020. Accessed December 9, 2021. https://www.cancer.org/cancer/colon-rectal-cancer/detection-diagnosis-staging/screening-tests-used.html

3 Davidson KW, et al. Screening for colorectal cancer: US Preventive Services Task Force recommendation statement. JAMA. 2021;325(19):1965-1977. 

4 Patel SG, May FP, Anderson JC, et al. Updates on age to start and stop colorectal cancer screening: recommendations from the US Multi-Society Task Force on Colorectal Cancer. Gastroenterol. 2022;162(1):285-299.

5 Shaukat A, Kahi CJ, Burke CA, et al. ACG clinical guidelines: colorectal cancer screening 2021. Am J Gastroenterol.2021;116:458-479.

 

Footnotes

a Data for gFOBT were collected from two studies (n=3503).

b Data for FIT were taken from 13 studies (n=44,887) of OC-Sensor family of FITs.

c Data for sDNA-FIT were based on 4 studies (n=12,424).

d Sensitivity data for colonoscopy came from 4 studies (n=4821), and specificity was reported from a single study.

e Data for CT colonography were based on 7 studies (n=5328).

f 95% confidence interval reported for all values

g Estimates are derived from modeling completed by the Cancer Intervention and Surveillance Modeling Network (CISNET) to inform the 2021 USPSTF recommendations. 

h Outcomes are expressed per 1000 40-year-olds who start screening at age 45 or at age 50.

i Average estimate across the three CISNET colorectal cancer models. See modeling report for additional details and model-specific estimates.

j Due to imprecision in sensitivity and specificity, there is considerable uncertainty in model predictions for HSgFOBT strategies. See modeling report for more information.

k Compared to other options for stool-based screening, these strategies do not provide an efficient balance of the benefits (life-years gained) vs. harms and burden (i.e., lifetime no. of colonoscopies) of screening. See modeling report for more information.

Last Updated: 3/13/2023