Colorectal Cancer Screening (PDQ®): Screening - Health Professional Information [NCI] - Evidence of Benefit
Mathematical models have been constructed to extrapolate the results of screening trials to screening programs for the general population in community health care delivery settings. These models project a reduction in CRC mortality or an increase in life expectancy using currently available screening methodology.[18,19,20,21] The anticipated success of such methodology is critically dependent on the appropriate use of the FOBT and an effective clinical management plan.[22,23]
A systematic review done through the Cochrane Collaboration examined all CRC screening randomized trials that involved gFOBT testing on more than one occasion. The combined results showed that trial participants allocated to screening had a 16% lower CRC mortality (RR = 0.84; 95% CI, 0.78–0.90). There was, however, no difference in all-cause mortality between the screened and control groups (RR = 1.00; 95% CI, 0.99–1.02). Furthermore, the trials reported a low positive predictive value (PPV) for the FOBT test, suggesting that most positive tests were false positives. From the trials with nonrehydrated slides (Funen and Nottingham), the PPV was 5.0% to 18.7%, while the PPV in the trials using rehydrated slides (Goteborg and Minnesota) was 0.9% to 6.1%. The report contains no discussion on contamination in the control arms of the trials and no information on treatment by stage.[24,25]
On initial (prevalence) examinations, from 1% to 5% of unselected persons tested with gFOBT have positive test results. Of those persons with positive test results, approximately 2% to 10% have cancer and approximately 20% to 30% have adenomas,[26,27] depending on how the test is done. Data from randomized controlled trials (RCT) are summarized in Table 3.
Table 3. Randomized Controlled Screening Trials: Fecal Occult Blood Testing
|Site||Population Size||Positivity Rate (%)||% Cancers Localizeda||Testing Interval||Relative Mortality Reduction|
|N/A = not available.|
|a % Localized = T1–3 N0 M0.|
| ||Screened||Control|| |
| ||Rehydrated: 9.8%|| || ||Biennial||21%|
|United Kingdom||150,000||Unrehydrated: 2.1%||52||44||Biennial||15%|
|Sweden||68,308||Unrehydrated: 1.9%||52||50|| ||16%|
| ||Rehydrated: 5.8%|| || || || |
Newer FOBTs: Nonrandomized Controlled Trial Evidence
The immunochemical FOBT (iFOBT) was developed to detect intact human hemoglobin. The advantage of iFOBT over guaiac FOBT (gFOBT) is that it does not detect hemoglobin from nonhuman dietary sources. It also does not detect partly digested human hemoglobin that comes from the upper respiratory or GI tract. Preliminary studies of several commercially developed iFOBT tests define their sensitivity and specificity compared with concurrently performed colonoscopy. These studies also examine these outcomes for different cut points, and the benefit of multiple versus single stool samples. Generally, iFOBT testing is more sensitive for cancers than for benign neoplasias. As expected, higher cut points decrease sensitivity and increase specificity.