Department of Medicine, Brigham and Women’s Hospital
Instructor in Medicine, Harvard Medical School
Colon cancer screening is extremely important. Unlike some other screening tests, this one actually prevents cancer. The important reason to do colon cancer screening is that we can find lesions before they become problematic and remove them. When we're doing a colonoscopy we're looking for polyps which are raised or flat lesions in the colon that look abnormal and that we're able to remove during the procedure.
Not all of these precancerous or adenomatous polyps will become cancer, though a vast majority of them have the ability to. So regardless, it's very important to get them out before they become an issue. We know that adenoma detection rates, or the rate in which we find polyps in people, is somewhere between 30 percent and 40 percent for men and 20 percent to 30 percent for women. Generally, a good percentage of people will have polyps on their exam and that's why we stress the importance of getting your colonoscopy during the recommended intervals.
Colonoscopy Screening Guidelines
Generally speaking, all guidelines recommend that colon cancer screening begin at age 50 and that's for the average-risk person. If you have a family history of colon cancer or other genetic risk factors, you should discuss these with your physician because screening may start earlier than age 50. But for the general population, colon cancer screening begins at age 50.
The interval in which you continue to have colonoscopies after that will determine what's found during your colonoscopy. So if you have no polyps, then the interval is every 10 years. If you have polyps, it may be sooner than that-- something like three to five years, depending on what's found.
We know that screening generally starts at age 50; however, determining when screening stops is on an individual patient basis. Most guidelines recommend screening stop between ages 75 and 85. If you are someone who has had multiple polyps removed in the past, it may be worth continuing screening in that ten year period.
Bowel preparation is actually the most important part of the exam because how clean your colon is on the inside is what allows us to see and remove polyps. Polyps can actually be small or flat and hard to detect if the colon isn't very clean.
Before a colonoscopy you’ll prepare by cleaning out your bowel with a bowel prep. That's a laxative that helps remove all the stool from your colon so that when we actually go in during the colonoscopy, we're able to see really well and find all the polyps.
We generally recommend going on a low fiber diet the week before, meaning avoiding raw vegetables or high fiber foods because those can actually hang around the colon for quite awhile and make cleaning of your colon more difficult. Altering your diet a week before your colonoscopy can make the prep more effective when you actually start to drink the laxative the day prior to the procedure.
When you come in for the procedure, you will have an IV placed in your arm and be given sedation that makes you sleepy and comfortable. We generally use something called IV conscious sedation, so you're not completely asleep like you would be for a surgery, for example, but you're very comfortable and almost in a twilight state. Then we take a long, thin camera that has a light on the end of it and we actually go in through the rectum and all the way around the colon. On the way back is actually when we do the examination. We also put air and water into the colon so that we can distend it and see really well. Colonoscopies generally last about 30 to 40 minutes, depending on how many polyps we have to remove and how clean the colon is.
Right now there is no proven therapy or proven intervention to prevent polyps. We are predisposed to polyps through mutations that are sporadic and so there's not necessarily anything one person can do to prevent them. That said, getting screenings, colonoscopies can certainly prevent cancers from happening from polyps.