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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

SitePopulation SizePositivity Rate (%)% Cancers LocalizedaTesting IntervalRelative Mortality Reduction
a % Localized = T1–3 N0 M0.
Minnesota[5,28]48,000Unrehydrated: 2.4%5953Annual33%
 Rehydrated: 9.8%  Biennial21%
United Kingdom[10]150,000Unrehydrated: 2.1%5244Biennial15%
Denmark[14]62,000Unrehydrated: 1.0%5648Biennial18%
Sweden[29]68,308Unrehydrated: 1.9%5250 16%
 Rehydrated: 5.8%    
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