Studies: Colon Cancer Screening Saves Lives

September 19, 2013

News Review From Harvard Medical School -- Studies: Colon Cancer Screening Saves Lives

Screening tests for colon cancer reduce deaths by one-third to one-half, 2 new studies find. The first study included nearly 89,000 health professionals. Researchers kept track of them for about 22 years. People who had a screening colonoscopy that found no problems were 56% less likely to die of colon cancer than those who had no screening tests. Colon cancer deaths were 40% lower for people who had a screening sigmoidoscopy that found no problems. Both tests look at the inside of the colon. A colonoscopy looks at the whole colon. A sigmoidoscopy looks at only the lower portion. A second study randomly divided 46,500 older adults into 3 groups. Two groups received fecal occult blood tests. This test looks for blood in the stool, which can indicate possible colon cancer. The third group received "usual care." Few people in this group got the test. Compared with the usual-care group, colon cancer deaths were reduced 32% for the group that got annual fecal occult blood tests and 22% lower in the group that got tests every 2 years. The New England Journal of Medicine published the studies. HealthDay News wrote about them September 18.

By Robert H. Shmerling, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

Screening for cancer may seem like a simple process:  Perform a test, find cancer early and cure it.

Yet it's not so simple. For many types of cancer:

• There is no test that can reliably detect cancer at a curable stage
• The available tests are not always accurate
• Testing may be invasive or risky
• Testing may be inconvenient, expensive or uncomfortable
• Some cancers (such as certain prostate tumors) are harmless, so detecting them is not helpful

Perhaps this explains why we have good screening tests for only a few types of cancer. These include cancers of the colon, breast and cervix.

For colon cancer, we have several screening tests. They include:

• Colonoscopy -- A doctor inspects the entire colon using a flexible tube with a light and camera at its tip. If a cancerous or precancerous tumor is seen, it can be removed.
• Sigmoidoscopy -- This is similar to a colonoscopy. However, only the last portion of the colon is inspected.
• Stool testing -- A sample of stool is tested for tiny amounts of blood. Blood may indicate the presence of colon cancer.

But there is uncertainty regarding just how much benefit these tests provide. Two new studies address these questions. They appear in the current issue of the New England Journal of Medicine.

In the first study, researchers kept track of nearly 89,000 adults for 22 years. Some had colonoscopy or sigmoidoscopy. Others had no screening. About 2% of the total group developed colon cancer, and 0.5% died of the disease.

In the other study, more than 46,000 adults were randomly divided into 3 groups. Two of the groups received stool testing -- every year or every 2 years.  A comparison group received "usual care," with a low rate of stool testing.  Screening occurred during two 6-year periods. Up to 30 years later, about 2% of the total group had died of colon cancer.

These studies concluded that:

• Colonoscopy and sigmoidoscopy were linked with a lower risk of colon cancer.  Over 22 years, those who had no problems found during a colonoscopy were about 56% less likely to develop colon cancer than those not screened. This risk reduction lasted up to 15 years. Those who had a polyp removed or had no problems found on a sigmoidoscopy were about 40% less likely to develop colon cancer.
• Only colonoscopy was linked with a lower risk of colon cancer in the upper colon.
• Adults screened by colonoscopy or sigmoidoscopy also had lower rates of death from colon cancer.
• Those having regular stool tests were less likely to die of colon cancer. Colon-cancer death rates were 1.8% in the annual screening group, 2.2% in those screened every 2 years and 2.7% for those not screened. This translated to a risk reduction of 32% for annual screening and 22% for screening every 2 years.

Taken together, these findings support current advice for adults to have a screening colonoscopy beginning at age 50. Sigmoidoscopy may be a worthwhile alternative, though its benefit was less. Doctors may recommend stool testing, too. But the ideal combination of tests has not been well studied.

People with average risk of colon cancer are advised to get a repeat colonoscopy every 10 years. These findings suggest that this may be more frequent than necessary.

Health care professionals and public health officials can use studies like these to encourage colon cancer screening.

What Changes Can I Make Now?

Do what you can to prevent colon cancer.

• Get screened. Talk to your doctor about when to begin testing, which test is best for you and how often to repeat it. Some people have a high risk of colon cancer. They include people with Crohn's disease or a strong family history of colon cancer. These groups may be advised to begin screening earlier and to repeat testing more often.
• Exercise more. Studies suggest that regular exercise may reduce the risk of colon cancer.
• Change your diet. A diet that is low in saturated fats may lower your cancer risk.
• Don't smoke. Cigarette smoking has been linked to many types of cancer, including colon cancer.

There is some evidence that taking a daily aspirin or folic acid may reduce the risk of colon cancer. However, this is not proven. Review these options with your doctor as well. 

What Can I Expect Looking to the Future?

We are likely to have better cancer screening tests in the future. However, a lot of research will be needed to prove their worth. A good example is lung cancer. Recent research suggests that CT scans may help to detect lung cancer in people at high risk.

Currently, the biggest challenge for colon cancer screening is getting people to get the available tests. You can expect to hear public health campaigns encouraging screening.  About 50,000 Americans die of colon cancer each year. This new research confirms that many of those deaths are preventable. So I am hopeful that screening will become more widespread.