Harvard Men's Health Watch

Colon cancer testing: What's in it for you?

Being checked for hidden colorectal cancer is a smart bet, though it's hard to say whether it will ultimately extend your life span.

Recently, the National Colorectal Cancer Roundtable—a national organization of medical groups, health care providers, government agencies, and patient advocates—launched the "80% by 2018" initiative. The goal is to convince more people to get screened for hidden colorectal cancer. Right now, about 65% of Americans do so.

If the 80% in 2018 initiative moves you to action, what benefit can you expect? Being screened with colonoscopy or some other method can identify precancerous growths, called polyps, on the colon wall. Once removed, polyps can't turn into cancer.

"There is now very compelling evidence that colonoscopy reduces death from colorectal cancer," says Dr. Andrew Chan, a gastroenterologist, colorectal cancer prevention researcher, and associate professor at Harvard Medical School.

Consider the uncertainties, too

It may sound like screening more people for colorectal cancer is a no-brainer, but there is more to it. True, removing polyps prevents cancer from happening down the road. But on the other hand, not all colon cancers prevented by screening ultimately turn out to be the cause of death in the generally older people who get most of them. Other causes, such as heart disease, may strike them sooner.

Right now, it's hard to pin down exactly how many lives are saved or extended with regular colorectal cancer screening. Furthermore, your lifetime chance of dying from colorectal cancer is 2% to 3%—substantially below the risk posed by heart disease.

But that doesn't mean screening isn't worth considering. Whatever your chance of developing colon cancer, research shows that early diagnosis and treatment cuts that risk by about half. Despite the uncertainties, colorectal cancer screening is a smart move.

Colonoscopy: The gold standard

Of several available screening methods, colonoscopy is considered the gold standard because it allows the doctor to both find and remove polyps. In this procedure, a doctor uses a flexible lighted instrument to examine the entire length of the colon for precancerous polyps.

Two-thirds of polyps are the precancerous type, called adenomas. Studies suggest that colonoscopy at age 50 will find adenomas in about 25% of men. Only about 5% of adenomas become tumors, and that process can take seven to 10 years or even longer.

The doctor doing the colonoscopy will remove all polyps observed, just to be sure. If your colonoscopy finds no polyps, you can wait up to 10 years until the next one. If polyps are discovered, you may need to return in three to five years.

Colonoscopy alternatives

Other screening methods can detect cancer or precancer in the colon and rectum, although not as thoroughly as colonoscopy does. These are the procedures typically offered in the United States:

Flexible sigmoidoscopy. A lighted instrument (sigmoidoscope) enables the doctor to examine the lower third of the colon, where most polyps occur. If any are found, the person usually has a full colonoscopy. Sigmoidoscopy has been shown to re-duce the chance of dying from colorectal cancer.

Stool testing. A sample of stool is examined for tiny traces of blood or DNA associated with cancer. Stool tests don't detect polyps unless they bleed, but if you have the test every year, it reduces the risk of death from colorectal cancer—although not as much as colonoscopy and sigmoidoscopy.

Virtual colonoscopy. A CT scan of the colon is performed to produce a three-dimensional image of the colon wall. If it shows potentially precancerous features, you will then have a colonoscopy. It's unclear whether virtual colonoscopy pre-vents death from colorectal cancer, but it appears to detect many of the larger polyps that colonoscopy finds.

Discuss the options for colorectal cancer screening with your primary care doctor. If you want to avoid colorectal cancer, any screening option is better than none.

When can you stop?

Older men must strike a balance between the potential risks and benefits of colorectal cancer screening. Most colonoscopies go off without a hitch, but the procedure does come with a small risk of bleeding and a one-in-2,000 chance of a small tear in the colon wall. The older you are, the greater the risk of experiencing some sort of adverse effect.

Also, understand that the full benefit of colonoscopy plays out over a decade or longer. "The older you are, the more likely you are to develop colorectal cancer, but also the less likely you are to benefit from screening, because of the overall shorter life expectancy," Dr. Chan says.

However, colonoscopy can still offer a benefit even to a man in his 80s—if he is generally healthy. The U.S. Preventive Services Task Force advises that everyone be screened until age 75, but that screening should stop after age 85, since the likelihood of benefit at that age is small. Men ages 76 to 85 at average risk might decide to cease colonoscopies if they have other, more serious or chronic medical problems that should be the priority.

How to reduce your risk of colorectal cancer

The major influences on cancer risk are age and family history. But these steps could reduce your overall chance of developing colorectal cancer:

  • Eat less meat. To lower your risk of cancer, eat a healthy diet, with minimal red meat—especially processed or cured meats. A recent World Health Organization review of past research concluded that people with meat-rich diets—especially those who eat a lot of processed or cured meats—face higher rates of colon cancer.
  • Take low-dose aspirin. Research strongly indicates that taking daily low-dose aspirin, which many men already do to prevent heart attacks and strokes, also reduces the chance of getting colorectal cancer. Most doctors would not advise taking aspirin solely to prevent colorectal cancer, however.
  • Get enough calcium. Research has also linked obtaining adequate calcium to a lower risk of colon cancer, but this, too, is uncertain. If you are already obtaining a healthy amount of calcium from your diet every day, it might offer an extra "bump" of cancer prevention.
  • Get enough fiber, just in case. Some studies have found that people with high-fiber diets get less colorectal cancer—perhaps because fiber helps clear the colon of cancer-causing toxins. But other studies have found no connection. Either way, fiber is great for regularity, and if you are eating a high-fiber diet you are probably eating lots of healthy fruits and vegetables.

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