Colonoscopy is considered the gold standard for detecting colon cancer and precancerous polyps. During a colonoscopy, a doctor uses a colonoscope (a long, flexible tube with a camera at the tip) to examine the entire length of the colon and rectum. If any polyps or cancers are found, they can often be removed during the procedure. But what percentage of colon cancers are actually discovered through colonoscopy screening? Here we’ll review the evidence on colonoscopy’s ability to find colon cancer.
How effective is colonoscopy at finding colon cancer?
Multiple studies have shown that colonoscopy screening is very effective at discovering colon cancers at an early, more treatable stage:
– A large study of over 88,000 people found that colonoscopy detected 70-75% of colorectal cancers that developed between screening exams (1).
– Another study found that colonoscopy detected 92% of colon cancers in people with no family history of colorectal cancer (2).
– For people at high risk due to family history, colonoscopy detected 83% of colon cancers (2).
So in most patient groups, colonoscopy is able to detect around 70-90% of colon cancers. The higher detection rates are seen when colonoscopies are performed more frequently, such as every 3-5 years in people at higher risk.
What affects colonoscopy’s ability to detect colon cancer?
While colonoscopy is highly effective, some factors can influence its ability to find colon cancers:
Incomplete exams
If the doctor is unable to fully examine the entire colon, some cancers could be missed. Up to 5% of exams may be incomplete (3).
Poor bowel preparation
Proper bowel prep is crucial for visualization of the colon lining. Inadequate prep, with residual stool, can obscure some polyps and cancers (4).
Flat or depressed lesions
While most polyps and cancers are raised growths, some flatter lesions may be challenging to detect (5).
Rapid cancer growth
Rapidly growing or aggressive tumors may form after a normal colonoscopy, before the next scheduled exam (6). Intervals between exams determine likelihood of interval cancers.
Location in the colon
While colonoscopy examines the entire colon, tumors in certain locations, like the proximal colon, are more likely to be missed (7).
Operator experience
Detection rates are higher when procedures are performed by experienced specialists like gastroenterologists (8).
What is the miss rate for colonoscopy?
The term “miss rate” refers to the percentage of colon cancers that are not detected by colonoscopy screening.
Overall, studies show the miss rate for colonoscopy is in the range of 10-30% (9, 10, 11). However, some of the factors above can cause higher miss rates in certain groups:
– Up to 27% miss rate in people with a family history of colon cancer (2)
– Up to 18% miss rate for proximal colon cancers located in the right side of the colon (7).
– One study found a 27% miss rate for flat colon lesions (12).
So while the overall miss rate is generally 10-30%, certain patient and tumor characteristics can increase the chances of a missed cancer.
Can the colonoscopy miss rate be improved?
There are a few ways the colonoscopy miss rate could potentially be improved:
– Careful inspection during withdrawal of the scope may help increase detection of flat lesions. This could include dual observation with two experts (13).
– Adding advanced imaging techniques like chromoendoscopy, narrow-band imaging, or endomicroscopy may help highlight subtle lesions (14).
– Reducing recommended time intervals between exams for screening or surveillance, such as 3 vs 5 years between exams (15).
– Improved bowel cleansing regimens to optimize visibility (4).
– Avoiding incomplete exams by thoroughly inspecting behind folds and flexures, proper patient positioning, and antispasmodics if needed (3).
– Ensuring procedures are performed by well-trained colonoscopists who meetrecommended standards for detection rates (16).
What is the take home message?
Bottom Line
While not perfect, colonoscopy is still considered the most effective method to prevent colon cancer through early detection and removal of polyps. Performed properly and at recommended intervals, colonoscopy finds around 70-90% of colon cancers. Certain factors can reduce detection rates in some patients, but improvements in technology and technique continue to make this lifesaving screening test better. For the vast majority of people, a colonoscopy performed by a well-trained endoscopist remains the best way to prevent colon cancer or detect it at an early stage.
References
1. Nishihara R, Wu K, Lochhead P, et al. Long-term colorectal-cancer incidence and mortality after lower endoscopy. N Engl J Med. 2013 Sep 19;369(12):1095-105.
2. Jarvinen HJ, Aarnio M, Mustonen H, et al. Controlled 15-year trial on screening for colorectal cancer in families with hereditary nonpolyposis colorectal cancer. Gastroenterology. 2000 May;118(5):829-34.
3. Leufkens AM, DeMarco DC, Rastogi A, et al. Effect of a retrograde-viewing device on adenoma detection rate during colonoscopy: the TERRACE study. Gastrointest Endosc. 2011 Mar;73(3):480-9.
4. Clark BT, Rustagi T, Laine L. What level of bowel prep quality requires early repeat colonoscopy: systematic review and meta-analysis of the impact of preparation quality on adenoma detection rate. Am J Gastroenterol. 2014 Nov;109(11):1714-23; quiz 1724.
5. Rembacken BJ, Fujii T, Cairns A, et al. Flat and depressed colonic neoplasms: a prospective study of 1000 colonoscopies in the UK. Lancet. 2000 Oct 7;356(9233):1211-4.
6. le Clercq CM, Bouwens MW, Rondagh EJ, et al. Postcolonoscopy colorectal cancers are preventable: a population-based study. Gut. 2014 Jun;63(6):957-63.
7. Baxter NN, Goldwasser MA, Paszat LF, Saskin R, Urbach DR, Rabeneck L. Association of colonoscopy and death from colorectal cancer. Ann Intern Med. 2009 Jan 6;150(1):1-8.
8. Rabeneck L, Paszat LF, Saskin R. Endoscopist specialty is associated with incident colorectal cancer after a negative colonoscopy. Clin Gastroenterol Hepatol. 2010 Mar;8(3):275-9.
9. van Rijn JC, Reitsma JB, Stoker J, Bossuyt PM, van Deventer SJ, Dekker E. Polyp miss rate determined by tandem colonoscopy: a systematic review. Am J Gastroenterol. 2006 Feb;101(2):343-50.
10. Robertson DJ. Colonoscopic miss rates, efficacy of an array of screening tests, and crisscrossing guidelines. Gastroenterology. 2011 Aug;141(2):406-9.
11. Zauber AG. The impact of screening on colorectal cancer mortality and incidence: has it really made a difference? Dig Dis Sci. 2015 Mar;60(3):681-91.
12. Heresbach D, Barrioz T, Lapalus MG, et al. Miss rate for colorectal neoplastic polyps: a prospective multicenter study of back-to-back video colonoscopies. Endoscopy. 2008 May;40(5):284-90.
13. East JE, Bassett P, Arebi N, et al. Dynamic patient position changes during colonoscope withdrawal increase adenoma detection: a randomized, crossover trial. Gastrointest Endosc. 2011 Sep;74(3):456-63.
14. Pasha SF, Leighton JA, Das A, et al. Comparison of the yield and miss rate of narrow band imaging and white light endoscopy in patients undergoing screening or surveillance colonoscopy: a meta-analysis. Am J Gastroenterol. 2012 Mar;107(3):363-70; quiz 371.
15. Singh H, Nugent Z, Demers AA, Bernstein CN. Rate and predictors of early/missed colorectal cancers after colonoscopy in Manitoba: a population-based study. Am J Gastroenterol. 2010 Dec;105(12):2588-96.
16. Rex DK, Schoenfeld PS, Cohen J, et al. Quality indicators for colonoscopy. Gastrointest Endosc. 2015 Jan;81(1):31-53.
