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What percentage of colon cancers are found with colonoscopy?

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.


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16. Rex DK, Schoenfeld PS, Cohen J, et al. Quality indicators for colonoscopy. Gastrointest Endosc. 2015 Jan;81(1):31-53.