Surveillance

Surveillance testing is a recurrent testing policy offered after positive diagnostic test results. The intent of surveillance is to monitor individuals more closely than they would be followed with routine screening since people who have tested positive in the past may be at higher risk for CRC than the rest of the population. The user may specify the frequency with which tests are offered to individuals in the surveillance program. The current default interval in this model is 5 years.

The surveillance testing process is similar to diagnostic testing. The person may choose to take the test or choose not to take the test. All individuals who require surveillance are offered the same test, which is a colonoscopy by default. The user may override the default, but the model assumes that the test has 100% specificity and that a polypectomy will be performed if polyps are detected. The possible side effects of death and perforation are the same as for a routine screening test.

If the person has lesions:

The model checks each lesion independently to see whether the surveillance test detects it. The probability that a surveillance test detects a lesion is controlled by the test’s sensitivity parameters, as described for the routine screening test. A positive test result occurs when the test detects at least one of the lesions, and a negative test result occurs when the test fails to detect every lesion present. Detected lesions that are polyps are removed immediately via a polypectomy. If a cancerous lesion is detected, the model assumes that any other cancerous lesions are also detected. Thus, a surveillance test will detect all cancerous lesions, and a person’s cancer stage at initial diagnosis is always the most advanced stage of any of his or her cancerous lesions.

If the person does not have lesions:

The test will always correctly produce a negative result because the model assumes that the diagnostic test has 100% specificity. That is, the surveillance test will never result in false positives.

After a positive surveillance test result, the person remains in the surveillance program. If any of the detected lesions were cancerous, then the person is eligible for cancer treatment.

After the person has completed surveillance, defined as having a negative (normal) test result, he or she will return to the routine screening schedule of 10 years. The model assumes that the individual’s modality of screening will always be colonoscopy once surveillance is completed. In addition, the individual is assumed to screen with higher compliance following surveillance. This is in accordance with behavioral data that suggests that once people are aware they are “high risk,” such as previously having a polyp detected and removed, they are more likely to comply with recommended health services, including cancer screening.