Colorectal Cancer Screening (PDQ®)–Health Professional Version
Evidence of Harms
Potential harms are associated with the modalities used to screen for colorectal cancer (CRC), some of which have sufficient evidence and some that do not.
Overview
The tables for each screening test below show the magnitude of burden for several categories of harms encountered along the screening cascade. The magnitude of harms is a combination of the frequency and severity of harm, as perceived by the patient.
Harms are defined broadly as any negative effect on individuals or populations resulting from being involved in the screening process (cascade) compared with not screening. Potential harms are organized according to the type of harm (e.g., physical, psychological, and hassle/opportunity costs) and when they occur in the screening cascade (e.g., screening test/workup; screening test/workup results; surveillance and surveillance results; and early treatment and overtreatment). For example, potential harms of screening colonoscopy include harms of the screening test itself (e.g., perforation and bleeding), results of the screening test (e.g., anxiety from an abnormal result), surveillance (e.g. harms of more frequent colonoscopies), and treatment (e.g. earlier treatment or overtreatment). For other colorectal cancer screening tests, there are also harms associated with the workup (e.g. colonoscopy for positive fecal occult blood test [FOBT]). A recent study of three major hospitals found evidence that 71% of endoscopes tested positive for bacteria after cleaning and high-level disinfection of the scopes. This raises concern for endoscopy-associated pathogen transmission and patient safety, although no patients were involved in the study and the implications for patients are unknown.[1] For all aspects of participating in the screening cascade, there are time/effort and opportunity costs (nonfinancial harms) for the patient. We do not include here any financial harms to the patient/family, nor any psychological harm from anticipation of future financial costs related to screening.
Evidence Summary
Colonoscopy
The potential physical harms of colonoscopy include adverse effects from the preparation and adverse effects from the procedure (colonic perforation and bleeding; effects of sedation).[4-6] A systematic review of 60 studies that assessed complications of colonoscopy screening in asymptomatic patients found infrequent serious morbidity, which comprised major bleeding (0.8/1,000 procedures; 95% confidence interval [CI], 0.18–1.63) and perforation (0.07/1,000 procedures; 95% CI, 0.006–0.17), and only minor and short-lasting psychological harms.[7] These complications can be serious, requiring hospitalization. Colonic perforation and serious bleeding occur more often with biopsy or polypectomy, with an overall average of three to five serious complications per 1,000 procedures. The physical harm of discomfort during the procedure has been reduced by sedation, although sedation has its own potential for physical harm (magnitude and severity uncertain due to insufficient evidence).
Physical harms are also associated with further steps in the screening cascade, including diagnosis of CRC (some large ecologic studies have shown an increase in suicide soon after diagnosis) and overdiagnosis/overtreatment due to treating lesions that would never have caused the patient important problems (evidence insufficient to determine magnitude and severity).
The potential psychological harms of colonoscopy include anticipation of the procedure and anxiety while awaiting the results of biopsy reports. For people with polyps, there may be increased distress in considering oneself at increased risk of CRC (evidence insufficient). For people newly diagnosed with CRC, many will experience increased anxiety and depression for at least 6 months, as prognosis and treatment are discussed (evidence insufficient).
The harm of time/effort and opportunity costs involved in moving through the demands of the screening cascade are present throughout the process (evidence insufficient to determine frequency and severity).
FOBT/immunochemical FOBT (FIT)
The potential physical harms of fecal-based testing include the same harms as for colonoscopy for people with a positive test who have been referred for diagnostic colonoscopy.
The potential psychological harms, as well as time/effort and opportunity costs are also similar to the description above for colonoscopy (refer to the Colonoscopy section in the Evidence of Harms section of this summary for more information).[8] These harms are associated with moving through the screening cascade, regardless of the initial screening test. Although it is highly likely that these psychological harms, plus time/effort and opportunity costs, do occur, the exact frequency and severity of these harms are uncertain due to insufficient evidence.
Sigmoidoscopy
The potential physical harms of sigmoidoscopy are considerably less than those of colonoscopy, with a less intensive preparation. Serious procedural complications occur in perhaps three in 10,000 sigmoidoscopies compared with in three in 1,000 colonoscopies.[3] There is usually no sedation with sigmoidoscopy, thus again lowering the potential for complications.
The potential psychological harms of sigmoidoscopy screening, as well as the time/effort and opportunity costs of screening, are the same as given above for other screening strategies.
Computed tomography colonography (CTC)
The potential physical harms due directly to the procedure of CTC are less than either colonoscopy or sigmoidoscopy, with rare procedural complications.[3] However, CTC does involve repeated radiation exposure, with uncertain associated harms, and it also detects a number of extra-colonic incidental findings.[9-13] Incidental findings have been detected in between 40% to 98% of CTCs, with a variable number of these considered significant enough to proceed with further diagnostic testing. As there is little evidence that early detection of any of these findings could improve health outcomes for patients, these findings may be considered as harms until proven otherwise.
The potential psychological harms or time/effort and opportunity costs for CTC are similar to the descriptions above for patients moving through the screening cascade (evidence insufficient to determine frequency and severity).
References
- Ofstead CL, Heymann OL, Quick MR, et al.: Residual moisture and waterborne pathogens inside flexible endoscopes: Evidence from a multisite study of endoscope drying effectiveness. Am J Infect Control 46 (6): 689-696, 2018. [PUBMED Abstract]
- Jonas DE, Russell LB, Sandler RS, et al.: Value of patient time invested in the colonoscopy screening process: time requirements for colonoscopy study. Med Decis Making 28 (1): 56-65, 2008 Jan-Feb. [PUBMED Abstract]
- Whitlock EP, Lin JS, Liles E, et al.: Screening for colorectal cancer: a targeted, updated systematic review for the U.S. Preventive Services Task Force. Ann Intern Med 149 (9): 638-58, 2008. [PUBMED Abstract]
- Lin JS, Piper MA, Perdue LA, et al.: Screening for Colorectal Cancer: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force. JAMA 315 (23): 2576-94, 2016. [PUBMED Abstract]
- Levin TR, Zhao W, Conell C, et al.: Complications of colonoscopy in an integrated health care delivery system. Ann Intern Med 145 (12): 880-6, 2006. [PUBMED Abstract]
- Warren JL, Klabunde CN, Mariotto AB, et al.: Adverse events after outpatient colonoscopy in the Medicare population. Ann Intern Med 150 (12): 849-57, W152, 2009. [PUBMED Abstract]
- Vermeer NC, Snijders HS, Holman FA, et al.: Colorectal cancer screening: Systematic review of screen-related morbidity and mortality. Cancer Treat Rev 54: 87-98, 2017. [PUBMED Abstract]
- Bobridge A, Bampton P, Cole S, et al.: The psychological impact of participating in colorectal cancer screening by faecal immuno-chemical testing--the Australian experience. Br J Cancer 111 (5): 970-5, 2014. [PUBMED Abstract]
- Kimberly JR, Phillips KC, Santago P, et al.: Extracolonic findings at virtual colonoscopy: an important consideration in asymptomatic colorectal cancer screening. J Gen Intern Med 24 (1): 69-73, 2009. [PUBMED Abstract]
- Yee J, Kumar NN, Godara S, et al.: Extracolonic abnormalities discovered incidentally at CT colonography in a male population. Radiology 236 (2): 519-26, 2005. [PUBMED Abstract]
- Hara AK, Johnson CD, MacCarty RL, et al.: Incidental extracolonic findings at CT colonography. Radiology 215 (2): 353-7, 2000. [PUBMED Abstract]
- Gluecker TM, Johnson CD, Wilson LA, et al.: Extracolonic findings at CT colonography: evaluation of prevalence and cost in a screening population. Gastroenterology 124 (4): 911-6, 2003. [PUBMED Abstract]
- Xiong T, McEvoy K, Morton DG, et al.: Resources and costs associated with incidental extracolonic findings from CT colonogaphy: a study in a symptomatic population. Br J Radiol 79 (948): 948-61, 2006. [PUBMED Abstract]
Changes to This Summary (03/06/2019)
The PDQ cancer information summaries are reviewed regularly and updated as new information becomes available. This section describes the latest changes made to this summary as of the date above.
Updated statistics with estimated new cases and deaths for 2019 (cited American Cancer Society as reference 2). Also revised text to state that from 2006 to 2015, colorectal cancer (CRC) incidence declined by 3.7% per year among adults aged 55 years and older; however, from 2006 to 2015, in adults younger than 55 years, CRC incidence rates have been increasing by 1.8% per year. Also revised text to state that from 2007 to 2016, mortality rates from CRC declined by 2.7% per year among adults aged 55 years and older but increased by 1% per year among adults younger than 55 years.
This summary is written and maintained by the PDQ Screening and Prevention Editorial Board, which is editorially independent of NCI. The summary reflects an independent review of the literature and does not represent a policy statement of NCI or NIH. More information about summary policies and the role of the PDQ Editorial Boards in maintaining the PDQ summaries can be found on the About This PDQ Summary and PDQ® - NCI's Comprehensive Cancer Database pages.
About This PDQ Summary
Purpose of This Summary
This PDQ cancer information summary for health professionals provides comprehensive, peer-reviewed, evidence-based information about colorectal cancer screening. It is intended as a resource to inform and assist clinicians who care for cancer patients. It does not provide formal guidelines or recommendations for making health care decisions.
Reviewers and Updates
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Levels of Evidence
Some of the reference citations in this summary are accompanied by a level-of-evidence designation. These designations are intended to help readers assess the strength of the evidence supporting the use of specific interventions or approaches. The PDQ Screening and Prevention Editorial Board uses a formal evidence ranking system in developing its level-of-evidence designations.
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The preferred citation for this PDQ summary is:
PDQ® Screening and Prevention Editorial Board. PDQ Colorectal Cancer Screening. Bethesda, MD: National Cancer Institute. Updated <MM/DD/YYYY>. Available at: https://www.cancer.gov/types/colorectal/hp/colorectal-screening-pdq. Accessed <MM/DD/YYYY>. [PMID: 26389266]
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