Follow-up exams at the right time are essential to prevent cancer from developing.
Colorectal cancer is one of the most preventable forms of cancer—if you are screened for hidden warning signs while you are still healthy. Screening finds precancerous growths on the colon wall, called polyps, which the doctor can then remove.
"They are not cancer, and most of them have not started to change into cancer," says Dr. John Saltzman, associate professor at Harvard Medical School and director of endoscopy at Brigham and Women's Hospital in Boston. "If you get them at the precancerous phase, they don't have a chance to grow and turn into cancer."
But you will need to come back for follow-up testing to see if more polyps turn up in the future. Here is what to expect.
What are polyps?
A colonoscope, the flexible device used to inspect the colon, can grab and snip off polyps if they are relatively small. The timing of follow-up depends on what kind of polyps the doctor finds, how many, and how big they are.
Hyperplastic polyps: These polyps are not precancerous. Doctors generally remove them anyway, just to be safe.
Adenomas: Many colon polyps are the precancerous type, called adenomas. It can take seven to 10 or more years for an adenoma to evolve into cancer—if it ever does. Overall, only 5% of adenomas progress to cancer, but your individual risk is hard to predict. Doctors remove all the adenomas they find.
Sessile serrated polyps: Once thought harmless, this type of adenoma is now known to be risky. These are also removed.
When to return for follow-up
After polyps are removed, you will need to return for an additional colonoscopy. There is a 25% to 30% chance that a repeat colonoscopy will find additional polyps. How soon you need to return for follow-up depends largely on the size of the polyps found in the first exam.
If the colonoscopy finds one or two small polyps (5 mm in diameter or smaller), you are considered at relatively low risk. Most people will not have to return for a follow-up colonoscopy for at least five years, and possibly longer.
If the polyps are larger (10 mm or larger), more numerous, or abnormal in appearance under a microscope, you may have to return in three years or sooner.
If the exam finds no polyps, "your cancer risk is essentially the average for the population, and you can wait 10 years for the next screening," Dr. Saltzman says.
How a colon polyp progresses to cancer
Get the best exam you can
Whenever you have a colonoscopy, you should have the highest quality exam possible so the doctor can find all the polyps. During the colon-cleansing "prep" before the colonoscopy, follow the instructions to the letter. Eating a low-fiber diet for four to five days may improve the quality of the prep, Dr. Saltzman says. That's because fiber gets stuck in the nooks and crannies of the colon wall and can block the doctor's view. For colonoscopy to prevent cancer, the doctor must find and remove as many precancerous growths as possible.
Reducing your risk
After polyp removal, certain steps may lower your risk of colon cancer:
Eat less meat: Eat a healthy diet, with minimal red meat—especially processed or cured meats. Studies suggest that people with meat-rich diets tend to have higher rates of colon cancer.
Aspirin: Some research suggests that taking aspirin may reduce overall colon cancer risk, but the evidence is not definite. If you need to take aspirin for your heart, then it may offer some protection for the colon.
Calcium: Research has also linked a calcium-rich diet to lower colon cancer risk, but this, too, is uncertain. If you are already eating a healthy calcium rich diet to preserve bone health, you might get an extra "bump" of cancer prevention.
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