Cancer of the colon: have you been screened?


Cancer of the colon and rectum is the third most common malignant cancer in men and in women in the US, and ranks second as a cause of death from cancer. 90% of cases occur in people over the age of 50. Hence, routine screening for colon cancer starts at age 50 in most people. There are some genetic disorders that can lead to an increase in the risk of colon cancer. Colon cancer at a younger age in a parent or a sibling, for example, could indicate a higher risk of colon cancer. However, the majority of people who are diagnosed with it do not have these risk factors. Low fiber, high fat or low vegetable/fruit diets may predispose to colon cancer, as may cigarette smoking.

Colon cancer very often arises from polyps in the colon, which in themselves are benign overgrowths of tissue. Fortunately, if polyps are discovered and removed, the risk of colon cancer declines significantly. The best test, then, is one that can detect polyps as well as cancer. Cancer that is detected early is more likely to be curable. Unfortunately, because of the size of the colon and its storage capacity, colon cancer may exist for many years before it is discovered, without causing any symptoms.

The available tests include stool testing for microscopic blood (misses most polyps and a substantial number of cancers, but it is easier to do); barium enemas, in which a liquid is put into the colon followed by x-rays (requires a preparation similar to that required for the colonoscopy, may miss some polyps and cancer, and requires a colonoscopy if anything is found); flexible sigmoidoscopy, in which the part of the colon closest to the anus is examined visually (the downside is that one does not examine all areas at risk for cancer); colonoscopy, in which the entire colon is examined visually, and virtual colonoscopy, in which contrast is given followed by a CT scan of the colon. The advantages of flexible sigmoidoscopy and colonoscopy are that any visible polyps or cancer can be biopsied and/or removed at the time of the procedure. While they are very safe procedures, there is a small risk of perforation of the colon. There are studies recently completed and on-going about virtual colonoscopy; while it is more comfortable than regular colonoscopy, and there are some suggestions that it might even be able to pick up cancers and polyps missed by regular colonoscopy, anything seen on virtual colonoscopy would then require a regular colonoscopy.

The interval for rechecking for cancer and polyps depends on the test; if only stool tests are done, it should be done yearly; if the flexible sigmoidoscopy is done, it should be accompanied by annual stool tests and repeated each 3 to 5 years; if colonoscopy is done, it can be done each 8 to 10 years. After age 75, screening may be stopped if prior screening has been negative, unless the patient is in exceptionally good health.

I recommend to my patients that they undergo a colonoscopy as the screening procedure of choice. You should discuss colon cancer screening with your doctor when you reach 50, or even older if you have not had this done.

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Dennis Oliver, MD