Colorectal cancer is the cause of the second highest number of cancer deaths in the United States. However, it is also one of the most preventable. This is because colorectal cancers start as a precancerous growths called polyps or adenomas. If adenoma polyps are detected early and removed, this prevents colorectal cancer from forming. The procedure for removing polyps is a colonoscopy.
March is Colorectal Cancer Awareness Month and a good time to review the recommendations for detecting and preventing this disease. Screening for colorectal cancer is recommended for everyone – both men and women – older than age 50. If you have a close relative such as a parent or sibling with a history of colorectal cancer or adenoma polyps, it is recommended that you start screening at age 40, or 10 years earlier than when your relative was diagnosed, whichever is sooner. For example, if your mother had colon cancer at age 45, you should be screened at age 35.
There are multiple possible tests for colorectal cancer screening. The most common test used in the U.S. is colonoscopy. This allows both detection and removal of pre-cancerous polyps during the same procedure. A recent study showed that having a colonoscopy with removal of an adenoma polyp cuts the risk of dying from colon cancer in half. This test requires a strong laxative to prepare the colon for the procedure, but the procedure itself is well tolerated since sedation is used. Not all colonoscopies are equally effective, a well-cleaned colon and a careful examination are important for detecting polyps. The national standard for detecting adenomas is to find them in 15-25 percent of screening colonoscopies. At the Vancouver Clinic, we detect adenomas in 45-66 percent of screening colonoscopies. Colonoscopy has a very low rate of complications, which will be discussed with you before the procedure.
Other colorectal cancer screening tests include testing stool samples with specialized cards that detect microscopic blood, sigmoidoscopy, and a specialized CT scan called CT colonography. All of these tests have advantages and disadvantages, and if any of them detect polyps or blood in the stool, a colonoscopy is recommended. Be aware that polyps do not bleed; therefore, stool cards detect colorectal cancer early, but they do not prevent it. Sigmoidoscopy and CT colonography are both unsedated examinations that also require a bowel preparation. These two tests have lower rates of adenoma detection than colonoscopy, but also have a lower rate of complications.
There are many options available for colorectal cancer screening. Discuss with your doctor which type is best for you. The important thing is to have a screening test performed, as colorectal cancer is both very common and very preventable.