Generally, screening for colorectal carcinoma is performed to prevent the development of cancer and to recognize and remove any premalignant lesions. Screening is justified when the disease is common and associated with significant morbidity and mortality, when the screening examinations are accurate enough to detect early forms of the disease in a manner that is acceptable to the patient, when the examinations can be performed in clinical practice, when detection leads to treatment that will improve prognosis, and when the potential benefits of screening outweigh the potential morbidity and costs. Evidence from various trials supports that screening for colorectal carcinoma meets these criteria. Generally, screening tests are evaluated in terms of performance, effectiveness, screening frequency, complications, and acceptability. Frequency of testing is usually determined by scientific evidence but also may be controlled by factors such as cost and risk.
Effectiveness basically describes how well a test works in routine practice.
Performance, simply stated, evaluates how well the test can differentiate between those likely to be positive and those less likely to be negative. For colorectal neoplasia, this means the presence or absence of polyps. For the purposes of colorectal neoplasia, screening must be distinguished from surveillance. Screening identifies those patients who are more likely to have polyps or cancer from among the asymptomatic population. Surveillance monitors those with a history of colorectal neoplasia or those with other higher risk conditions such as inflammatory bowel disease.