A new study suggests that more use of colonoscopy has helped to reduce U.S. rates of colorectal cancer. Colonoscopy looks at the upper and lower colon. It uses an instrument that can remove as well as find cancers. It also can snip out polyps before they turn into cancers. In 2001, Medicare began to pay for people to get a screening colonoscopy every 10 years. Colonoscopies greatly increased after this decision. Surgeries for cancer in the upper colon were steady until 2002. Then they dropped 3.1% a year through 2009. Colonoscopy is the only test that looks at the upper colon from the inside. Surgeries for cancer in the lower colon also fell faster after 1999. In the next decade, they dropped by 3.8% per year. Researchers said the increase in colonoscopies may be one cause. Taking out polyps may have prevented many cancers, especially in the upper colon. The journal Gastroenterology published the study. HealthDay News wrote about it October 23.

By Howard LeWine, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

Recently, there has been a lot of debate about how useful cancer screening tests really are. Of all of them, experts disagree most about routine PSA testing in men age 50 and over to detect early prostate cancer.

A mammogram every year or other year for women age 50 and older has broader acceptance. But some studies suggest that life-saving benefits of mammography are overstated.

On the other hand, screening tests for colorectal cancer and cervical cancer have the most solid evidence to support them. And very few experts suggest we should not be doing these tests.

The reason for this difference is that PSA tests and mammograms don't prevent cancer. They only detect early cancers. Colonoscopy and Pap detect not only early cancers but also pre-cancers. This leads to treatment to stop them from becoming cancers.

Not all early prostate and breast cancers turn out to be harmful. This is especially true for prostate cancer. Most prostate cancers found because of a high PSA blood level never shorten life or affect quality of life. Today, many men with early prostate cancer can be safely watched without treatment.

Early detection improves outcomes for some types of breast cancer -- but not all. Some women who have surgery probably don't need it. We are less sure about which cancers can just be watched. So they all get removed.

Clearly cervical cancer screening with Pap smears has greatly reduced the number of women who develop the disease. We have suspected that colorectal cancer screening will do the same. And the results of this new study strongly support this assumption. Researchers from Stanford University School of Medicine did the study.

Cancer of the lowest part of the colon -- the rectum and the area just above it – was already on the decline before widespread use of screening colonoscopy. This lower area of the colon could be directly examined with a sigmoidoscope. If polyps were seen during the exam, they could be removed. Removing polyps stops them from turning into cancers.

In 2001, Medicare approved payment for screening colonoscopy to look at the entire colon. The number of people getting colonoscopy rose dramatically. The researchers collected information about screening and colon cancer rates among more than 2 million people. Between 1993 and 2009, the number of colorectal cancer cases dropped by 33%. This drop was mostly related to screening sigmoidoscopy.

Cancers of the upper part of the colon are beyond the reach of the sigmoidoscope. The rates of these cancers did not change from 1993 to 2002. But a colonoscopy can find and remove upper colon polyps that can turn into cancers. As colonoscopies grew, from 2002 to 2009, "upper" colon cancers fell by 3.1% per year.

What Changes Can I Make Now?

Colonoscopy is the best screening test for colorectal cancer. It is recommended once every 10 years for people age 50 and over who have an average risk of colorectal cancer.

The doctor uses a flexible, lighted instrument called a colonoscope. You receive medicine to help you relax and avoid discomfort. The doctor looks through the colonoscope and inspects the colon.

If the doctor finds a pre-cancerous polyp, a device on the end of the colonoscope is used to remove it. Removing pre-cancerous polyps helps prevent them from turning into cancers. If you have a polyp, your doctor will advise you not to wait 10 years for the next colonoscopy. How soon you should have it again depends on what the doctor finds.

Colonoscopy does have risks. It's possible that the instrument can puncture the colon. Feces could get into the abdomen through this hole. This could cause an infection called peritonitis. It's also possible to have excessive bleeding if the doctor removes a polyp or snips a bit of tissue for a biopsy. Fortunately, these risks are small.

Other screening methods exist for colorectal cancer. But they are more likely to miss pre-cancerous changes in the colon. And if one of these tests finds something suspicious, you'll still need a colonoscopy. This includes CT colon scans, with or without laxatives.

If you opt not to do colonoscopy, you should choose another screening method. But realize that if the test is positive, you will still need colonoscopy. The options include:

• Sigmoidoscopy every 5 years -- This test is similar to colonoscopy, but it looks at only the lower part of the colon. No sedation is necessary and the preparation is much simpler.
• Fecal occult blood stool testing every year
• A combination of sigmoidoscopy every 5 years and fecal occult blood testing every year
• Virtual colonoscopy -- This test uses a CT scan instead of a scope to check the colon for cancers and polyps. It is not covered by Medicare.
• Stool DNA testing (not covered by Medicare)

What Can I Expect Looking to the Future?

Colonoscopy is expensive. It also carries risk. In the future, a simpler and cheaper test that could reliably find polyps before they become cancerous would be ideal. Then only those people with a positive, easy test would need colonoscopy.