___________________________________________________________________________ Colorectal Cancer
COMMON COLORECTAL CANCER SCREENING TESTS There are several screening tests available for colorectal cancer, with varying levels of efficacy and clinical utility ( Table 4 ). Of these, the criterion standard is colonoscopy. Colonoscopy With screening colonoscopy, a colonoscope (a thin tube with a light and video camera on one end connected to a display monitor) is inserted through the rectum and guided through the length of the colon for observation on the monitor screen. Instruments to remove polyps and obtain biopsy are inserted through the rectum as needed [131]. Colonoscopy allows direct visualization of the colonic mucosa, lesion biopsy, and polyp removal over the entire colon. The sensitivity and specificity for colorectal cancer and advanced adenomas are very high, and colonoscopy is the confirmatory test used with all other screening approaches when positive findings occur [120]. Potential Complications and Harms Colonoscopy may fail to detect as many as 6% of colorectal malignancies, and the miss rate for adenomas smaller than 1 cm has ranged from 12% to 17% [132]. This is largely the result of high inter-operator variability in adenoma detection rate. Greater awareness of this hazard from inadequate colonoscopy performance has led to heightened emphasis on training and continuous quality assurance of endoscopists [120]. In addition, colonoscopy is an invasive procedure, requires an invasive bowel cleansing, is time-consuming and uncomfortable, and thus possesses several characteristics that negatively affect patient acceptance as a first-line screening test [120].
Clinically significant complications that require medical intervention are rare and include perforation, bleeding, and cardiovascular events. Complication rates may increase in older patients [133; 134]. More than 85% of serious colonoscopy complications occur during polypectomy, and a study of 97,000 colonoscopies found polypectomy associated with a seven-fold increase in risk of bleeding or perforation [135]. Up to 33% of patients report one or more minor, transient gastrointestinal symptoms after colonoscopy, and a review of 12 studies involving 57,742 colorectal cancer screening colonoscopies in average-risk patients found the aggregate rate of serious complications was 2.8 per 1,000 procedures [134; 136]. Recommendations to Optimize the Adequacy of Colonoscopy Bowel Preparation The U.S. Multi-Society Task Force on Colorectal Cancer has published guidelines for adequate pre-colonoscopy bowel cleansing [137]. The goals of this consensus document are to provide expert, evidence-based recommendations for clinicians to optimize colonoscopy preparation quality and patient safety. The adequacy of pre-procedure bowel cleansing merits special attention because this patient factor is strongly associated with colonoscopy success. Up to 20% to 25% of colonoscopies are attempted in patients with inadequate bowel preparation, leading to diminished adenoma detection rates, longer procedural time, lower cecal intubation rates, and increased electrocautery risk [138; 139; 140]. Patient risk factors for inadequate preparation include older age, male sex, higher BMI, history of inadequate preparation, history of constipation, and use of opioids or other constipating medications. Patients with complex past medical histories or current conditions, including previous gastric or colonic
EFFICACY OF COLORECTAL CANCER SCREENING TESTS
Screening Approach
Magnitude of Effect
Effect on colorectal cancer mortality reduction Fecal occult blood test (FOBT)
15% to 33%
Sigmoidoscopy
About 25% to 50% for left colon
Digital rectal examination
No effect
Colonoscopy
About 60% to 70% for left colon, uncertain for right colon
Effect on surrogate endpoints (e.g., stage at diagnosis, adenoma detection) Sigmoidoscopy
45% decrease in cancer detection rate vs. colonoscopy
FOBT/sigmoidoscopy
No difference between sigmoidoscopy and FOBT vs. sigmoidoscopy alone
Barium enema
Detects 30% to 50% of cancers detected by colonoscopy
Colonoscopy
About 3% of patients with no distal adenomas have advanced proximal neoplasia, with a 3-fold increase in this rate in patients with distal adenomas
Computed tomography colonography
May have similar sensitivity to colonoscopy
Stool DNA mutation tests
Unknown
Immunochemical FOBT
60% to 90% of colorectal cancers
Source: [1]
Table 4
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