Effectiveness of Colonoscopy Screening for Colorectal Cancer
Effectiveness of Colonoscopy Screening for Colorectal Cancer
The effectiveness of colonoscopy screening is measured by the magnitude of the effect on CRC incidence and mortality on a population level (ie, in those offered the test or in those eligible for the test). Thus, these measures should be determined on the entire target population for screening, besides those undergoing colonoscopy. Therefore, one of the major determents of effectiveness is that individuals in the target population accept the test (ie, undergo the colonoscopy; see figure 1).
(Enlarge Image)
Figure 1.
Effectiveness of colonoscopy screening. The effectiveness of colonoscopy screening to reduce colorectal cancer incidence and mortality is determined by the four domains: compliance, efficacy, quality and treatment.
Measuring the effect of colonoscopy only in those who actually undergo the test is appealing because it would, theoretically, give a better estimate of how good the test is in preventing cancer and cancer-related death. However, these analyses are subject to the so-called healthy-screenee bias and, thus, not trustworthy. Healthy-screenee bias is a form of selection bias and occurs frequently because individuals with a lower CRC risk (ie, the most healthy) are more prone to adhering to screening, while higher-risk individuals (ie, the unhealthy, such as smokers) do not attend the screening. Measurement of CRC incidence or mortality in those attending versus those not attending, or not offered screening in this setting, would result in an overestimate of colonoscopy's ability to reduce cancer, while the observed difference is rather due to different baseline risks.
As figure 1 illustrates, in addition to patient compliance, the effectiveness of colonoscopy screening is determined by the efficacy of colonoscopy in reducing cancer incidence and mortality in those who underwent the colonoscopy; the quality of the colonoscopy service and individual endoscopist (determined by indicators such as adenoma detection rates (ADR), caecum intubation rates, quality of bowel preparation, and complication rates). Finally, the treatment of lesions detected at screening must result in better prognosis than treatment at a later (clinical) stage. This requires that the prognosis of CRC is related to the stage at diagnosis (early stages better prognosis than late stage) and that treatment of early (screening detected) stages is possible.
What Is Effectiveness?
The effectiveness of colonoscopy screening is measured by the magnitude of the effect on CRC incidence and mortality on a population level (ie, in those offered the test or in those eligible for the test). Thus, these measures should be determined on the entire target population for screening, besides those undergoing colonoscopy. Therefore, one of the major determents of effectiveness is that individuals in the target population accept the test (ie, undergo the colonoscopy; see figure 1).
(Enlarge Image)
Figure 1.
Effectiveness of colonoscopy screening. The effectiveness of colonoscopy screening to reduce colorectal cancer incidence and mortality is determined by the four domains: compliance, efficacy, quality and treatment.
Healthy-screenee Bias
Measuring the effect of colonoscopy only in those who actually undergo the test is appealing because it would, theoretically, give a better estimate of how good the test is in preventing cancer and cancer-related death. However, these analyses are subject to the so-called healthy-screenee bias and, thus, not trustworthy. Healthy-screenee bias is a form of selection bias and occurs frequently because individuals with a lower CRC risk (ie, the most healthy) are more prone to adhering to screening, while higher-risk individuals (ie, the unhealthy, such as smokers) do not attend the screening. Measurement of CRC incidence or mortality in those attending versus those not attending, or not offered screening in this setting, would result in an overestimate of colonoscopy's ability to reduce cancer, while the observed difference is rather due to different baseline risks.
Determinants of Effectiveness
As figure 1 illustrates, in addition to patient compliance, the effectiveness of colonoscopy screening is determined by the efficacy of colonoscopy in reducing cancer incidence and mortality in those who underwent the colonoscopy; the quality of the colonoscopy service and individual endoscopist (determined by indicators such as adenoma detection rates (ADR), caecum intubation rates, quality of bowel preparation, and complication rates). Finally, the treatment of lesions detected at screening must result in better prognosis than treatment at a later (clinical) stage. This requires that the prognosis of CRC is related to the stage at diagnosis (early stages better prognosis than late stage) and that treatment of early (screening detected) stages is possible.
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