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Colon or bowel cancer is second only to lung cancer as a killer in Canada. First of all, less than 12 percent of these cancers are hereditary. There are two types of hereditary colon cancers: FAP (Familial Adenomatous Polyposis) and HNPCC (Hereditary Nonpolyposis Colon Cancer). You need to have at least two close relatives with positive genetic results to consider this possibility. You might then meet the criteria to have a gene test performed on a blood sample. Prevention is all cases is simple on paper. Since 80 percent of colon cancers arise from polyps, and 25 percent of polyps will become malignant within 20 years time, removing all bowel polyps over 1 cm in size would substantially reduce colon cancers. But how does one know that you have a painless, symptomless polyp? That's where screening comes in. Screening is not a method of diagnosis. It reduces spending by identifying people at higher risk. As my colleagues are painfully aware, in Canada we don't have the resources to offer colonoscopy to all who may benefit, so we try to identify the group that may benefit most.
There are several screening methods in use today. FOBT (fecal occult blood test) is the oldest and least sensitive. It checks for microscopic blood in stool by smearing small samples on a paper slide. Samples from at least two separate days increase the detection rate. A positive FOBT means more testing and nothing else. Studies using a variation of this test are attempting to use a genetic trait of some cancers, called MSI (microsatellite instability) to detect abnormal cells found in stool. The DRE (digital rectal exam) performed by your doctor is also considered a screening test, and used more so for prostate cancer. A DCBE (double contrast barium enema) is an X-ray technique to exam the entire colon with the aid of contrast material. Sigmoidoscopy is a quick view of the last part of the colon using a flexible camera. Colonoscopy also uses the flexible camera to view the entire colon. It depends on a skilled operator and also on the patient being properly cleaned out so that the view is not obscured by fecal material. Anyone who has had one will tell you that the worst part is not the test, but the preparation. But it does carry the distinct advantage of providing intervention and sometimes cure at the time of performance. Polyps can be removed, and suspicious areas sampled at the time of testing. Risks include a small chance of bleeding or perforation. The criteria for colonoscopy are evolving yearly, and currently include rectal bleeding, previous polyp history, change in bowel habits, first degree relatives with colon cancer, and other inflammatory bowel problems such as ulcerative colitis.
There are a few newer methods available privately at cost and may involve travel. One is CT-Colography. It employs a CAT-Scan machine that rotates around the torso to produce multiple images that become reconstructed into a 3-D virtual tour through the bowel. Another new technology is the Capsule Camera. This large pill with a micro camera inside is swellowed, and images are transmitted to a belt pack while the "pill" travels through the alimentary tract. In both cases, one drawback is that a positive test will still require a follow-up colonoscopy. A blood test for colon cancer is in development and may be available in the USA soon.
Prevention in the end narrows down to the simplicities. All persons aged 50 and above should be screened. Eating fresh fruits and vegetables, exercising three times weekly, minimizing alcohol intake and avoiding tobacco and toxins are a sensible start.
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