Colorectal Cancer Screening (PDQ®): Screening - Health Professional Information [NCI] - Evidence of Benefit
Table 3. Randomized Controlled Screening Trials: Fecal Occult Blood Testing continued...
The impact of adenoma detection rates (ADRs) was assessed in a health maintenance organization in follow-up after 314,872 colonoscopies done from 1998 to 2010 by 136 gastroenterologists, each of whom had done at least 300 colonoscopies during that period. The goal was to determine rates of interval CRC, interval advanced CRC, and CRC death and to relate those rates to a gastroenterologist's ADR. There were 712 interval cancers (155 advanced) and 147 CRC deaths. The risk of interval cancer from lowest to highest quintile of ADR was 9.8, 8.6, 8.0, 7.0, and 4.8 per 10,000 person-years of follow-up. The adjusted hazard ratio, for physicians in the highest quintile compared with the lowest, was 0.52 for any interval CRC, 0.43 for advanced CRC, and 0.38 for fatal CRC. Each 1.0% increase in ADR was associated with a 3% decrease in risk of cancer, although the CI for each quintile was broad. Limitations of the study include the inability to determine which specific feature of ADR led to reduced interval cancer; for example, it is unclear whether it was due to the following:
- Removal of small adenomas that may grow rapidly to become CRC.
- ADR being a surrogate outcome for an endoscopist's ability to more completely remove adenomas.
- ADR being a surrogate outcome for an endoscopist's ability to better detect large flat serrated lesions.
- Higher ADR leading to recommendations for more frequent postpolypectomy surveillance colonoscopy.
Another limitation is that harms of colonoscopy associated with ADR could not be measured.
Evidence about colorectal cancer mortality reduction
Although there is no RCT to assess reduction of CRC incidence or mortality by colonoscopy, some case-control evidence is available. Based on case-control data about sigmoidoscopy, noted above, it has been speculated in the past that protection for the right colon might be similar to that found for the left colon. However, a recent case-control study of colonoscopy raises questions about whether the impact of colonoscopy on right-sided lesions might be different than the impact on left-sided lesions. Using a province-wide administrative data base in Ontario, investigators compared cases of persons who had received a diagnosis of CRC from 1996 to 2001 and had died by 2003. Controls were selected from persons who did not die of CRC. Billing claims were used to assess exposure to previous colonoscopy. The OR for the association between complete colonoscopy and left-sided lesions was 0.33, suggesting a substantial mortality reduction. For right-sided lesions, however, the OR of 0.99 indicated virtually no mortality reduction.