Guide to colon cancer prevention

Screening tests such as colonoscopy can cut the risk dramatically

Published: March 2012

During a colonoscopy, doctors can detect and remove polyps (shown here in red).

Prevention strategies and screening tests could help cut the number of deaths in the U.S. from colorectal cancer—if only people took full advantage of them. As it is, only 65 percent of the adults who should be screened actually are, a government survey found. And even with many screening and prevention strategies, colorectal cancer remains the second leading cause of cancer-related deaths in the U.S. for both men and women. (Lung cancer is the first.)

A survey of 3,357 men and women published in the May 2010 issue of the American Journal of Preventive Medicine found that the top three reasons for not getting screened for colorectal cancer were:

  • The failure of a health-care professional to suggest testing.
  • A lack of awareness about whether they should be screened.
  • A belief that testing is too costly.

(Under the health-care reform law passed in 2010, Medicare and new private insurance plans are required to cover most types of colorectal cancer screening with no co-payments or deductibles.)

People in the survey also said they avoided colorectal cancer screening because they considered it “too embarrassing” or feared the results. Among those who had undergone a colonoscopy, the biggest obstacle to being screened again was the dread of preparing for it.

In 2011, about 141,000 people in the U.S. were given a diagnosis of colorectal cancer, and the disease will cause 49,000 deaths.

Although better screening and treatment have resulted in almost a 3 percent drop in mortality rates each year since the late 1990s, nearly half of the cases are diagnosed at a late stage, when treatment is less likely to be lifesaving.

A highly preventable cancer

Colorectal cancer usually develops over 10 to 15 years without causing symptoms. Most cases start as noncancerous polyps in the lining of the large intestine or its final segment, the rectum. Detecting and removing polyps prevents them from developing into cancer. Screening tests, such as colonoscopy, can reveal not only cancer but also precancerous growths, which can be removed early.

“We are talking about the opportunity to prevent cancer from occurring,” says Durado D. Brooks, M.D., M.P.H., director of prostate and colorectal cancer programs for the American Cancer Society.

The five-year survival rate for early-stage colorectal cancer is 90 percent if the disease is detected while still localized. Survival drops to 10 percent in cases discovered after the cancer has spread to other organs. Researchers estimate that 1,900 deaths could be prevented for every 10 percent increase in the number of people being screened.

Additionally, a study in the Jan. 4, 2011, issue of the Annals of Internal Medicine found that colonoscopies cut the risk of colon cancer by 77 percent over 10 years, which is higher than some previous studies found. Better technology and training might explain that improvement, researchers say.

Keep in mind that there are several screening tests available, and a positive result doesn’t necessarily mean you have cancer. Stool tests can return false positives because of bleeding from noncancerous conditions, such as hemorrhoids, ulcers, infections, or inflammatory bowel disease.

Questionable findings revealed by stool testing, sigmoidoscopy, or CT colonography should be confirmed by a colonoscopy. During that test, a doctor can remove any polyps or take biopsies of suspicious growths.

How to prepare for screening

With some screening options, it’s critical to take steps to ensure accurate results.

If you’re having a colonoscopy or CT colonography, your preparation must be thorough to provide clear views. If you don’t prepare well enough, you might have to repeat the preparation and procedure.

During the 24 hours before the test, you’ll need to restrict your diet to clear liquids, such as broth; dessert gelatin that’s not purple, blue, or red; clear juices; clear soda; and black coffee or tea (no cream or sugar). You also have to swallow a laxative solution, which could be as much as a gallon. To overcome the solution’s taste, chill it, suck on lime after each glass, or ask your doctor whether it’s OK to add lemon, lime, or ginger.

Ask for laxatives with polyethylene glycol (Golytely, Halflytely, Miralax); avoid sodium-phosphate laxatives (OsmoPrep, Visicol), which pose a risk of kidney damage. A week before the procedure, stop taking iron supplements, and avoid nonsteroidal anti-inflammatory drugs such as aspirin or ibuprofen (Advil and generic) because they can cause gastrointestinal bleeding. In fact, talk to your doctor about any prescription or over-the-counter drugs you take and ask whether you should stop before the test. Try to schedule colonoscopy exams as early in the day as possible, when doctors’ skills at finding polyps tend to be at their best.

If you opt for the guaiac-based stool test, which screens for fecal blood, be aware that certain foods and medicine can ruin its accuracy. Three days before the test, stop consuming red meat, cantaloupe, uncooked broccoli, turnips, radishes, horseradish, and vitamin C supplements. Fecal immunochemical stool tests don’t require dietary or medication restrictions.

Adopting an anti-cancer lifestyle

Screening tests find incipient colorectal tumors, but various studies suggest that the following diet and lifestyle changes could eliminate up to 40 percent of colorectal cancer:

  • Eat less red meat. During digestion, red and processed meats form carcinogenic chemicals. The colorectal cancer risk was 22 percent greater among people who ate 5 ounces of red and processed meat a day compared with those who ate less than an ounce a day, according to a 2011 meta-analysis combining results of 21 studies.
  • Eat more vegetables, fruit, and fiber. A recent study using data from the U.S. Polyp Prevention Trial looked at the impact of diet on 1,900 people with a history of precancerous polyps. Those who met goals for cutting fat and consumed at least 18 grams of fiber and 3.5 servings of fruit and vegetables per 1,000 calories each day were 35 percent less likely to develop new polyps during the study.
  • Exercise. Sedentary people are about twice as likely to develop colorectal cancer as highly active exercisers. Aim for at least 30 minutes a day of moderately intense exercise.
  • Maintain a healthy weight. Being overweight increases the risk of colorectal cancer no matter how active you are.Excess abdominal fat (indicated by a waist size that exceeds 35 inches for women and 40 inches for men) could be a more important risk factor than overall body weight.
  • Don’t rely too much on drugs or supplements. Some, such as aspirin and related NSAIDs, calcium supplements, and for women, postmenopausal hormone therapy, might lower risk, evidence shows. But all pose additional health risks, and there’s not enough proof of their effectiveness and safety to recommend routine use to prevent colon cancer.
  • Limit alcohol. People who average two to four drinks a day have a 23 percent higher risk than those averaging less than one drink a day.
  • Don’t smoke. Researchers have enough evidence to conclude definitively that smoking tobacco contributes to colorectal cancer. And women appear to be more susceptible to precancerous polyps from smoking than men, according to a study published online in July 2011 in the journal Digestive Diseases and Sciences.

Know the warning signs

Colon cancer might not cause symptoms until it reaches an advanced and deadly stage. but small, treatable cancers and even precancerous polyps can develop between screenings and cause symptoms you shouldn’t ignore.

For example, a growing polyp can bleed or start to block the intestine. Talk with your doctor if you notice any of these warning signs:

• Blood in the toilet or on tissue after a bowel movement.
• Cramping pain in the lower abdomen.
• Unexplained weight loss or fever.
• Constipation or diarrhea that lasts for more than several days.
• Stools consistently colored dark or black,* or narrow in shape.
• Discomfort or the urge to have a bowel movement when there’s no need to have one.

Don’t ignore warning signs. Pay attention to your instincts and be prepared to advocate for follow-up testing.

* Note that iron supplements and medicine such as bismuth subsalicylate (Pepto-Bismol and generic) can color stools black. Foods such as beets can make stools appear blood-red for days.
Editor's Note:

This article first appeared in the December 2011 issue of Consumer Reports on Health under the headline "Stopping a Treatable Cancer."

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