A shared decision-making process for selecting a screening modality is a key to patient compliance and timely detection and treatment.
Home Tests: FOBT and FIT
Low to moderate sensitivity
Large randomized controlled trials demonstrate a decrease in CRC mortality of up to 33 percent.12–13, 51–53
Annual fecal occult blood test (FOBT) is 24 percent sensitive for advanced adenomas or colorectal cancer.54
Annual fecal immunochemical tests (FITs) use antibodies to detect human hemoglobin, and are not affected by diet or medications.13, 55–57
FIT significantly improves the sensitivity and specificity to 91 percent and 88 percent respectively for colorectal cancer detection.55 Change to FIT slightly increased colon cancer screening rates.58
The rate of positive results from FIT does not decrease after repeated colorectal cancer screening, but the positive predictive value of the FIT for advanced neoplasia and for colorectal cancer is significantly lower among second-round participants who tested negative in the first round.59
- Easy, safe, convenient
- FIT detects colon cancer and advanced adenomas with increased sensitivity compared with the FOBT.
- FOBT: heat stability is excellent and cost is less compared to other methods.
- FIT and FOBT must be repeated annually to be beneficial.
- Standard FOBT requires dietary restrictions and multiple samples. Positive tests require colonoscopy and (possibly) other testing.
- The Hemoccult Sensa II™ is more sensitive, but has a lower specificity compared with Hemoccult II™.
- FIT vary in sensitivity and specificity.57
- Requirement for three day testing with FOBT is less convenient than the single day for FIT.
Moderate sensitivity and specificity
Two randomized controlled trials, one from the United kingdom and one from the United States, documented a decrease in mortality for distal colorectal cancer of about 50 percent after 11 years of follow-up when an initial screening flexible sigmoidoscopy is performed.20–21
Flexible sigmoidoscopy detects 70–80 percent of all CRC and large adenomas.60
Approximately two percent of patients with normal findings on flexible sigmoidoscopy have a significant lesion in the proximal colon.60–61
The risk of perforation is less than 1 in 1,000.62–63
- Safer and more convenient than colonoscopy
- Takes about 10 minutes to perform and is usually well-tolerated without sedation
- Most patients can drive home alone or return to work following the procedure.
- Requires bowel preparation with enemas
- If adenomas found, further testing with colonoscopy is required to visualize the complete colon and remove polyps
- Does not visualize most of the colon; some lesions will be missed
High sensitivity and specificity
In cross-sectional screening studies, colonoscopy is more sensitive than FOBT, or flexible sigmoidoscopy combined with FOBT, for detecting large adenomas and CRC.60–61
Evidence from the National Polyp Study shows that patients who had adenomas removed during participation in the study had a 53 percent reduction in mortality from colon cancer over a median of 15.8 years. This supports the hypothesis that colonoscopic removal of adenomatous polyps prevents death from colorectal cancer and this prevention is long term.18
The benefit of colonoscopy is significant for decreasing mortality from left-sided colorectal cancer but not as strong for right-sided cancers.11, 48–49
In U.S. studies, the overall risk of perforation was approximately 2 in 1,000, but lower if polypectomy was not performed.62–63 The risk for perforation increases with increasing age and the presence of two or more comorbidities.62
The endoscopist’s adenoma detection rate is an independent predictor of the risk of interval colorectal cancer and is considered a major quality indicator for the colonoscopic procedure.41
- Colonoscopy has the ability to detect and remove polyps at the time of the initial examination. Polypectomy has been shown to decrease colon cancer mortality.18
- Enables direct visualization of the entire colon when evidence—via landmarks—indicates the cecum was reached
- Colonoscopy requires an orally administered bowel preparation.
- The exam takes about 30 minutes plus additional recovery time.
- Patients need to be escorted home and are advised not to go back to work the same day if sedation is given.
- Unlike home stool testing and sigmoidoscopy, no randomized trials of colonoscopy have shown benefit in decreasing CRC mortality. Observational studies show a benefit of ~50 percent decrease in mortality that is similar to randomized studies of sigmoidoscopy.
- Mortality from proximal colon cancer, as compared to left-sided colorectal cancer, may be affected to a lesser degree by the performance of screening colonoscopy.11, 43
CT Colonography (“Virtual Colonoscopy”)
High sensitivity and specificity
In a study of asymptomatic adults, CT colonographic screening identified 90 percent of patients with colon cancer or adenomas 10mm or larger in diameter.66–67 Laxative-free colonography has been reported, but is not routinely available.68
CT colonography does not offer the ability to remove polyps and prevent cancer.
CT colonography should not be a modality of choice for high-risk patients with polyp syndromes or inflammatory bowel disease given its inability to detect flat lesions with accuracy or to remove polyps.
Recently MR colonography has also been shown to detect colon cancers and polyps with accuracy.70
- Fast (10–15 minute), noninvasive imaging of the entire colon69
- Sedation is not required; patients may drive home or return to work the same day.
- Some patients find CT colonography to be more acceptable than standard colonoscopy.
- Detection of some significant extra-colonic findings (mostly abdominal aortic aneurysms and renal cell carcinomas)
- Variability in sensitivity based on technique and experience of the radiologists
- Requires bowel preparation similar to colonoscopy (at present)
- Requires a rectal tube to insufflate air into the colon, which can cause cramping
- Exposure to radiation
- Abnormal findings require a standard colonoscopy
- Can miss small and flat adenomas
- Detection of some incidental extra-colonic findings may lead to additional testing that otherwise would not have been done.