What is the optimal interval for screening colonoscopy after diagnosis of a colorectal adenoma?

Colorectal cancer (CRC) remains one of the most common causes of death in industrialized countries. The incidence rates vary among different populations, but are higher in males than females and increase with age. Obesity, diabetes, cigarette smoking, high alcohol consumption, eating red meat (particularly processed meat), and lack of physical activity are all recognised risk factors. Colorectal cancer is potentially amenable to secondary prevention by screening, because the detection and removal of an adenomatous polyp can prevent colorectal cancer from subsequently developing. In addition, when CRC is diagnosed while still localized (i.e., confined to the wall of the bowel), 5-year survival is likely to be extremely favourable in the region of 90%, but falls to 66% for stage II (i.e. disease with lymph node involvement). Hence, the principle of the benefit of colonsocopic screening is widely accepted. Yet the large numbers of colonoscopies required demands considerable resources, and existing guidelines tend not to provide estimates of resource implications.