Cancer of the colon affects nearly one in 20 adults. Regular screening is the best way to prevent death from colon cancer. Most colon cancers arise from polyps, which are small outgrowths from the surface of the colon.
Although the great majority of colon polyps are harmless, over time (at least 5 or 10 years) some may become cancerous. There are many different tests that can be used to screen for pre-cancerous polyps and cancers. If performed regularly every five years, these tests can prevent any new lesions from reaching an advanced or dangerous stage. Most guidelines recommend that from the age of 50, one of the following screening tests should be considered:
Flexible Sigmoidoscopy – a flexible, lighted tube about the thickness of a finger with a small video camera on the end is inserted into the rectum to view the lower 60cm of the colon.
Air Contrast Barium Enema – barium sulfate is pumped into the colon using a small, flexible tube inserted into the rectum. When the colon is half full, air is pumped into the colon through the same tube. The barium then coats the surface of the colon and any bumps or projections from the bowel surface can be easily identified.
CT Colonscopy (virtual colonoscopy) – a CT scanner takes many pictures as it rotates around the body and a computer combines these pictures into detailed images of the inside of the colon and rectum to look for polyps or cancer.
Any suspicious or positive test result can then be followed up with a colonoscopy, where the whole colon can be visualized and, if necessary, a biopsy taken for further examination. For individuals with an increased risk, such as those with a strong family history, a regular colonoscopy should be considered as a first-line screening test.
Another approach to screening for colon cancer is based on the finding that polyps and colon cancers bleed easily, meaning that microscopic quantities of blood are lost into the stool. This is called occult blood loss, as it cannot be seen by the naked eye. However, occult blood loss can be detected by sensitive tests of stool samples. If stool tests are performed on multiple occasions (usually annually), they significantly reduce the rate of cancer deaths by facilitating early detection. The more compliant an individual is with testing and the more regularly they have the test done, the better the outcomes.