Colorectal cancer

Abstract

Adenomatous polyps are the known precursors of the majority of colorectal cancers, with the risk of malignancy increasing with increasing polyp size. Detection of these polyps followed by polypectomy has been found to prevent the development of colorectal carcinoma. Despite the screening test options currently available, the majority of people who should undergo screening for colorectal cancer do not do so. Four screening tests are routinely used for the detection of colorectal cancer. Current colorectal cancer screening options include faecal occult blood testing, flexible sigmoidoscopy, air-contrast barium enema examination and fiberoptic colonoscopy, whilst a more recently introduced test consists of er colonography. The faecal occult blood test is safe and inexpensive. However, its performance is poor, since most colon cancers bleed intermittently and most adenomatous polyps do not bleed. The sensitivity of the faecal occult blood test as a single test for colorectal cancer is 20%-30% and for a large polyp is 10%-15%. The sensitivity of this test for colorectal cancer increases with repeated screening and ranges between 72% and 78%. Many causes of false-positive results exist, such as upper gastrointestinal tract sources of bleeding. However, randomised controlled trials have shown that the faecal occult blood test confers a 15%-33% mortality reduction from colon cancer.